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Astrophysics Seminars From 2015 - 2016


Summer 2015

June 24, 2015

NOTE: Special Astro Seminar @ 4:00 -
SERF 383
 "Mapping the ISM in 3 dimensions with Pan-STARRS1 and 2MASS"

Douglas Finkbeiner
Professor of Astronomy and of Physics, Department of Physics
Harvard University

 2D emission-based maps have been used for decades to estimate the reddening and emission from interstellar dust, with applications from CMB foregrounds to surveys of large-scale structure. For studies within the Milky Way, however, the third dimension is required. I will present the status of our work on a 3D dust map based on Pan-STARRS1 and 2MASS over 3/4 of the sky, assess its significance compared to other dust maps, and say how we plan to approach the next step: R_V.

Fall 2015

September 30, 2015

 "Energetic Particles & Their Radiative Yields in Clusters"

Yoel Rephaeli
Research Scientist -and- Professor, School of Physics & Astronomy
UCSD-CASS -and- Tel Aviv University, respectively

 The galaxy population in a rich cluster includes many star-forming and radio galaxies. Energetic electrons and protons diffusing out of these galaxies traverse the magnetized intracluster (IC) gas and interact with ambient radiation fields, emitting in the wide range from radio to gamma ray. I will present results of detailed modeling of IC spectro-spatial distributions of galactic energetic electrons and protons and their radiative yields. Comparison of results of our calculations with radio 'halo' measurements, and upper limits on X-ray and gamma ray emission, suggests that galactic energetic electrons and protons can account for the range of observed IC non-thermal phenomena, weakening the need to invoke efficient particle (re)acceleration outside galaxies.

October 7, 2015

 "Probing the Epoch of Reionization with the TIME-Pilot [CII]
Intensity Mapping Experiment"

Abigail Crites
Keck Postdoc Fellow

 The epoch of reionization (EoR) is still a largely unknown period in the history of our universe and is an exciting frontier for scientific discovery. The Tomographic Ionized Carbon Intensity Mapping Experiment (TIME-Pilot) is a new millimeter-wavelength imaging spectrometer being designed to probe the EoR. This novel cryogenic instrument is a pathfinder for a new technique for studying the EoR through intensity mapping of the 157.7 um ionized carbon ([CII]) emission line. Specifically it is designed to detect [CII] clustering fluctuations and test the predicted [CII] amplitudes of faint emission from the earliest dwarf galaxies. The TIME-Pilot instrument will be sensitive to a wavelength range of ~200 - 300 GHz with R = 100, which will allow us to measure the redshifted 157.7 um [CII] line from z of 5 to 9, key redshifts for probing the EoR. It will also robustly detect CO clustering at low z (~1-3). [CII] intensity mapping offers a unique way to measure faint sources, which will be difficult to detect individually with JWST and ALMA. This method is also complimentary to other intensity mapping experiments such as 21-cm instruments that measure neutral matter rather than an ionized medium during the EoR. Measurements from TIME-Pilot will test the viability of the [CII] intensity mapping technique and a detection of the [CII] signal would set a strong foundation for building more sensitive line intensity mapping instruments for both ground- and space-based platforms.

October 14, 2015

 "The Surprisingly Complex Lives of Massive Galaxies and the Stability
of the Mass Fundamental Plane"

Rachel Bezanson
Hubble Postdoc Fellow
University of Arizona

 Once thought to be relics of a much earlier epoch, the most massive local galaxies are red and dead ellipticals, with little ongoing star formation or organized rotation. In the last decade, observations of their assumed progenitors have demonstrated that the evolutionary histories of massive galaxies have been far from static. Instead, billions of years ago, massive galaxies were more compact and morphologically different, possibly with more disk-like structures and many were still forming stars. The details of this observed evolution can place constraints on the physical processes that have driven massive galaxy evolution through cosmic time. I will discuss recent observational studies of the structural and dynamical properties of massive high-redshift galaxies. Specifically, I will demonstrate that in spite of their dramatic structural evolution, the mass fundamental plane, or the empirical relation between dynamics, sizes, stellar mass surface density of massive galaxies, has been in place since z~2. This relation appears to hold for massive galaxies of all types, not just red, dead ellipticals. Therefore, this scaling relation is an ideal tool to follow the evolution of galaxy populations through cosmic time. Finally, I will describe two ongoing spectroscopic surveys, CHOMP and LEGA-C, that will probe massive galaxy evolution since z~1.

October 21, 2015

 "Breaking Relativity: The Why and How of Lorentz Violation"

Matthew Mewes
Assistant Professor, Physics Department
Cal Poly, San Luis Obispo

 Lorentz invariance lies at the foundations of all known physics. However, attempts to formulate an ultimate theory of everything suggest that Lorentz invariance may be slightly broken. This idea has led to numerous searches for Lorentz violation, ranging from modern versions of the classic Michelson-Morley experiment to tests involving the orbit of the Moon. The current best tests of Lorentz invariance are those that search for tiny defects in the propagation of light that has traveled cosmological distances. Astrophysical observations are probing nature at the very limits of our understanding and may help uncover some of the Universe's biggest secrets.

October 28, 2015

 "The Frequency and Composition of Small Exoplanets"

Courtney Dressing
Sagan Postdoc Fellow

 Over the past twenty years, ground- and space-based investigations have revealed that our galaxy is teeming with planetary systems and that Earth-sized planets are common. I will focus on the results of the NASA Kepler mission and describe two investigations of the frequency and composition of small planets. First, we analyzed Kepler observations of small stars and measured a cumulative planet occurrence rate of 2.45 +/- 0.22 planets per small star with periods of 0.5-200 days and planet radii of 1-4 Earth radii. Within a conservative habitable zone based on the moist greenhouse inner limit and maximum greenhouse outer limit, we estimated an occurrence rate of 0.15 (+0.18/-0.06) Earth-size planets and 0.09 (+0.10/-0.04) super-Earths per small star habitable zone. Second, we explored the compositional diversity of small planets by using the HARPS-N spectrograph on the Telescopio Nazionale Galileo to measure the masses of transiting planets. Concentrating on the set of small planets with well-constrained masses and radii, we found that all dense exoplanets with masses of approximately 1-6 Earth masses are consistent with the same fixed ratio of iron to rock as the Earth and Venus. Future measurements of the masses and radii of a larger sample of planets receiving a wider range of stellar insolations will reveal whether the fixed compositional model found for these highly-irradiated dense exoplanets extends to the full population of low-mass planets.

November 4, 2015

 "Sweating the small stuff: simulating dwarf galaxies, ultra-faint dwarf galaxies,
and their own tiny satellites"

Coral Wheeler
Graduate Student
UC Irvine

 If LCDM is correct, then all dark matter halos hosting galaxies, from those hosting dwarfs to those hosting giant clusters, are filled with abundant substructure down to very low mass scales (<< 10^9 Msun). Specifically, even the dark matter halos of Local Group field dwarfs should be filled with subhalos, many of which should be fairly massive (~ 10^8 Msun), and thus are potential targets for hosting small (ultrafaint) galaxies. Here we make predictions for the existence of ultrafaint satellites of dwarf galaxies using the highest resolution cosmological dwarf simulations yet run (mgas~ 250 Msun). We simulate four halos — two each at the mass of classical dwarf galaxies (Mvir ~10^10 Msun) and ultrafaint galaxies (Mvir ~ 10^9 Msun) — down to z=0 using the GIZMO (Hopkins 2014) code. This code relies on state-of-the-art MFM hydrodynamics and implements the FIRE (Feedback in Realistic Environments) recipes (Hopkins et al. 2014) for converting gas into stars and capturing the energy fed back from those stars into the surrounding medium. We predict that ultrafaint galaxies (M* ~ 3,000 Msun) should exist as satellites around more massive dwarf galaxies (M* ~ 10^6 Msun) in the Local Group. These tiny satellites, as well as the two isolated ultrafaints, have uniformly ancient stellar population (> 10 Gyr) owing to reionization-related quenching. The more massive systems, in contrast, all have late-time star formation. Our results suggest that Mhalo ~ 5 x10^9 Msun is a probable dividing line between halos hosting reionization "fossils" and those hosting dwarfs that can continue to form stars in isolation after reionization. Importantly, we show that the extended ~50 kpc regions around Local Group “field” dwarfs may provide efficient search locations for discovering new ultrafaint dwarf galaxies, and discuss the prospects for their discovery in light of the new generation of large surveys and giant telescopes. If these tiny satellites are observed, this would provide evidence that dark matter substructure is truly hierarchical, as predicted in the standard paradigm.

November 11, 2015

NOTE: No Seminar Today (UCSD closed for Veteran's Day holiday)

November 18, 2015

 "The new era of percent-level nuclear rates for astrophysics"

Kenneth Nollett
Assistant Professor, Department of Physics

 Astrophysical models of hot environments require nuclear rates as inputs, and these rates are a challenge for both theory and experiment to determine. Nuclear theory has traditionally not provided astrophysics with predictive tools of high precision, but rather with a set of approximate tools for fitting and interpolating the data emerging from nuclear laboratories. However, at least for the light nuclei important in the Sun, the big bang, and neutrino-driven winds, the situation is shifting. Experimental precision has improved in recent years, driven by improved techniques and by the need for higher precision in these astrophysical environments. Nuclear theory, too, is undergoing a revolution in methods. There are new opportunities to make its traditional task of data-fitting more systematic. However, the most important development is the arrival of first-principles models of nuclei as collections of realistically-interacting neutrons and protons. Theory is now providing predictions that are competitive in precision with laboratory data and arguably more useful for astrophysical calculations. I will provide examples of these developments and discuss prospects for the near future, emphasizing my own work on first-principles models and on applying methods from quantum field theory to make nuclear data fitting more systematic.

November 25, 2015

NOTE: No Seminar Today (due to Thanksgiving holiday)

December 2, 2015

 “See the Sound: In Search of the Electromagnetic Counterparts to
Gravitational Waves”

Mansi Kasliwal
Assistant Professor of Astronomy

 The era of advanced gravitational wave (GW) interferometers has just begun. Hearing neutron star mergers may soon even be routine. Seeing the electromagnetic (EM) counterparts would enable measurement of basic astrophysical properties such as the luminosity, energetics, redshift and host galaxy environment of strong-field gravity events. Furthermore, it would serve as a litmus test for whether or not these mergers are indeed the long sought site of r-process nucleosynthesis (and produce half the elements heavier than iron). However, the challenge is unambiguously identifying the predicted faint, fast and possibly red counterpart in the coarse GW localizations. I present an ongoing Caltech EM-GW search motivated by end-to-end simulations. I also present the rapidly growing inventory of optical and infrared transients in the local universe that are fainter, faster and rarer than supernovae. New classes of transients have bridged the luminosity gap between novae and supernovae and represent missing pieces in our understanding of the fate of massive stars and the evolution of compact binaries. The next frontier in gap transients is the discovery of an EM-GW merger. The surge of EM-GW excitement may literally be dubbed the 21st century gold rush.

December 9, 2015

NOTE: NOTE: Today's seminar will be held in SERF 329
 "Tidal disruptions of stars by supermassive black holes: dynamics,
light, and relics"

James Guillochon
Einstein Postdoc Fellow
Harvard-Smithsonian CfA

 Most supermassive black holes in the local universe lie dormant, with only one in a hundred accreting at their Eddington limits. Aside from this active minority, and the black holes in nearby galaxies that we can observe to influence the dynamics of stars and gas, most remain difficult to study. Tidal disruptions of stars by supermassive black holes give these dormant black holes a chance to be seen once every ~10,000 years, and each tidal disruption brings along with it a host of observable signatures that can be studied from gigaparsecs away, from the moment of the disruption to millennia after a disruption has occurred. In my talk I will present work I have done on tidal disruptions of stars, and describe their dynamics, observational signatures from real-time monitoring, and relics of disruption that may exist in plain sight.

Winter 2016

January 6, 2016

 "Collapse and Star Formation in Self-gravitating Turbulent Fluids"

Norm Murray
University of Toronto

 Observations of star forming regions in the Milky Way have established that stars form in large molecular clouds or GMCs. The spectral lines of these GMCs are usually interpreted as the signature of turbulent motion. The kinetic energy in the turbulence is similar to the gravitational binding energy of the GMC. Work over the last decade, including research done in Heidelberg, suggests that stars form in converging flows in this turbulence. I will describe recent analytic and numerical work that has resulted in a detailed description of the evolution of such converging flows. I will show that the flows set up density structures that do not vary with time; the converging gas flows through fixed run of density onto a central star or star cluster. The collapse drives turbulent motions, resulting in deviations from Larson's Law (the size-linewidth relation), and slowing the inflow velocity below the free-fall rate. However, the infall velocity is proportional to the square root of stellar mass, resulting in a mass accretion rate that grows linearly with time.

January 8, 2016

NOTE: Special Astro-Plasma-CER Seminar Today @ Noon in SERF 383
(Pizza provided)
 "New Frontiers in Simulating Black Hole Accretion and Jets"

Alexander Tchekhovskoy
Einstein Postdoc Fellow, Department of Astronomy
UC Berkeley

 Black holes are responsible for a wide variety of astrophysical phenomena. They devour stars, eject relativistic jets, affect star formation and galaxy evolution, and enrich the Universe with heavy elements. In the next several years, the Event Horizon Telescope will produce resolved images of infalling gas and jets on the event horizon scale that promise to revolutionize our understanding of black hole physics. However, until recently, no first-principles models to quantitatively interpret these observations existed. I will present the first such models, the simulated spectra and images, and the constraints on the near event horizon physics coming from the comparison to the observations of the supermassive black hole at the center of our galaxy. I will then use simulations to constrain black hole physics in several other astrophysical contexts. I will finish by making connections to my future research plans.

January 13, 2016

 "Searching for Other Earths"

Elisa Quintana
Research Scientist
NASA AMES Research Center and SETI Institute

 This year marks the 20th anniversary of the first exoplanet discovered to orbit another star like our Sun. The field of exoplanets has since progressed dramatically, with a large part due to the success of NASA’s Kepler Mission, which has discovered and confirmed over 1,000 planets in our galaxy to date. Kepler’s primary goal is to determine the frequency of Earth-sized planets in the habitable zones (HZ) of other stars, regions within which a planet could sustain liquid water on its surface. In April 2014, we announced the discovery of Kepler-186f, the first Earth-sized planet found to orbit in the HZ of a star other than our Sun. While Kepler-186f is comparable to Earth in terms of size and the amount of starlight it receives, it orbits an M dwarf, a star that is smaller and cooler than the Sun.

I will present our work on the discovery and confirmation of Kepler-186f and will present new models on how these planets may have formed. M dwarfs present a new set of challenges for planetary habitability, as planets orbiting in their HZs are subject to stellar flares, high speed impacts, and they orbit close enough to their star that they may become tidally locked. I will discuss our current knowledge on the potential habitability of planets around M dwarfs, and will compare their challenges to those faced by other HZ planets that have been discovered around other stars that are more like our Sun. More than 70% of the stars in our galaxy are M dwarfs and therefore finding and characterizing Earth-size planets orbiting in their HZ has big implications for determining the frequency of other Earths.

January 20, 2016

NOTE: Special Astro Seminar Today @ 2:00 in SERF 383
 "New frontiers in Cosmology"

Yacine Ali-Haimoud
Postdoc Fellow, Department of Physics & Astronomy
Johns Hopkins University

 Exquisitely sensitive measurements of Cosmic Microwave Background (CMB) fluctuations have made it possible to determine with great precision the Universe’s inventory, as well as basic properties of its initial conditions. This required a highly accurate theoretical modeling of the underlying physics, in particular of the cosmological recombination process, which I will describe in the first part of this talk. A wealth of new and complementary data will be collected in the decades to come, promising spectacular advances in our yet very incomplete understanding of the cosmos. In the remainder of this talk, I will highlight some fundamental questions that upcoming cosmological probes will help us answer. I will first describe how massive neutrinos affect the growth of large-scale structure, an effect that will be used to determine their mass. I will then discuss CMB spectral distortions, a powerful probe the Universe’s early thermal history, and illustrate how they can be used to constrain the properties of the yet unknown dark matter particle. I will conclude by describing the exciting prospects of high-redshift 21-cm cosmology, in particular for characterizing the Universe’s initial conditions.

January 20, 2016

NOTE: (Regular seminar @ 4:00 in SERF 383)
 "X-ray binaries in the NuSTAR age: reflection, cyclotron lines, and variability"

Felix Fuerst
Postdoc in Physics

 The Nuclear Spectroscopic Telescope Array, launched in 2012 June, is the most sensitive hard X-ray telescope today. With its unprecedented spectral and spatial resolution above 10keV it is ideally suited to study the physics of compact objects in our galaxy. I will give a short introduction to the instrument and then discuss two main topics of the NuSTAR binaries program: Compton reflection spectra of black holes and cyclotron line formation in the strong magnetic field of neutron stars.

The reflection spectrum close to a black hole is subject to its strong gravity, which can be used to study the spin and environment around it. Relativistic distortions of the iron K-alpha line and the Compton hump between 10-20keV allow us to measure the inner radius of the accretion disk. The size of the inner disk radius in the hard state is a long-standing issue and I will present new measurements that show a slight truncation of the disk and discuss the spectral evolution during state transitions.

In accreting neutron stars the formation of cyclotron resonance scattering features allows us to directly measure the magnetic field strength close to their surface. These lines are typically found between 10-50keV and their shape and energy depend on the geometry of the magnetic field as well as on luminosity. New results using fast time-resolved spectroscopy show a correlation between the line energy and the X-ray flux at lower luminosities than predicted by theory. I will present different explanations for this behavior. Furthermore, with NuSTAR we could for the first time measure a significant deviation from a smooth line shape and I will discuss implications of this result.

January 22, 2016

NOTE: Special Astro Seminar Today @ Noon in SERF 383 (Pizza provided)
 "Mapping the Cool Baryons: Toward a Physical Picture for Galaxy Evolution”

Kate Rubin
Clay Postdoc Fellow
Harvard-Smithsonian CfA

 Current models of galaxy formation require that the buildup of galactic stellar mass proceeds at a rate much slower than the rate at which gas is accreted onto dark matter halos, with only ~6% of the cosmic energy density of baryons ending up in stars at z~0. QSO absorption line experiments indicate that the environments extending several hundred kiloparsecs from typical galaxies serve as massive reservoirs for the remaining material; however, the mechanisms which prevent the cooling and collapse of this diffuse baryonic component remain poorly understood. I will discuss my efforts to constrain the physics of galaxy formation by developing a set of empirical measurements of the incidence, mass, spatial distribution, and energetics of outflowing and accreting gaseous material around galaxies. Using novel experimental design currently viable only with the Keck and Very Large Telescopes and the new SDSS-IV/MaNGA survey, I will present unique constraints on the surface density and size of metal-enriched regions around galaxies, as well as analysis of the spatially-resolved kinematics of cool material along the line of sight to galaxies over the past ~8 billion years. Finally, I will discuss the potential of these observational techniques, used in combination with next-generation optical facilities, to revolutionize our understanding of the processes regulating galaxy growth.

January 27, 2016

 "Reconciling Dwarf Galaxies with LCDM Cosmology"

Andrew Wetzel
Caltech & Carnegie Observatories

 Low-mass "dwarf" galaxies trace structure formation on the smallest cosmological scales and represent the most significant challenges to the cold dark matter (CDM) model. However, because they reside in low-mass halos with shallow gravitational potential wells, dwarf galaxies also are highly sensitive to baryonic processes. Because these faintest galaxies are readily observable only within the Local Group of the Milky Way (MW) and Andromeda (M31), it is critical to understand and model their formation within the environment of a MW-like host. I will introduce The Latte Project, a new suite of cosmological zoom-in hydrodynamic simulations that model the full formation history of a MW-like galaxy at parsec-scale resolution, using the FIRE (Feedback in Realistic Environments) model for star formation, stellar evolution, and stellar feedback. For the first time, this simulation also self-consistently resolves the internal structure of the satellite dwarf galaxies that form around a MW-like host, including the relevant baryonic physics to predict their stellar populations. I will present first results from this ultra-high-resolution simulation suite, addressing the long-standing "missing satellites", "core-cusp", and "too-big-to-fail" problems of LCDM cosmology. I also will discuss the dramatic impact of stellar feedback on the stellar populations within dwarf galaxies, including promising new avenues for using upcoming observations to test feedback models.

February 3, 2016

 "Studying the origin of the Milky Way nuclear star cluster one star at a time"

Tuan Do

 Due to its proximity, the Milky Way nuclear star cluster provides us with a wealth of data not available in other galactic nuclei. In particular, we can observe the properties of individual stars. These properties include the position in two dimension and the velocity in three dimensions. With the rapid advances integral field and multi-object spectroscopy, we can also derive the physical properties of individual stars, such as the effective temperature, abundances, and surface gravity. I will discuss how the pass decade of adaptive optics measurements from Keck and Gemini have been used to derive physical properties of the cluster through dynamical models and luminosity functions. While these analyses have been very successful at helping us understand its structure and star formation, there is still enormous untapped potential in these data sets. I will discuss new work on the physical properties of the stars, such as their metallicity, and how they will help us understand the origin and evolution of the nuclear star cluster.

February 10, 2016

 "Using Cosmic Telescopes to Study Dusty, Star-Forming Galaxies"

Gregory Walth
Postdoctoral Scholar

 Dusty star forming galaxies (DSFGs), characterized by their far-infrared (far-IR) emission, undergo the largest starbursts in the Universe, contributing to the majority of the cosmic star formation rate density at z = 1 − 4. The Herschel Space Observatory for the first time was able observe the full far-IR dust emission for a large population of high-redshift DSFGs, However, Herschel reaches the confusion limit quickly and only the brightest galaxies at redshifts z > 2 can be detected. With gravitational lensing, we are able to surpass the Herschel confusion limit and probe intrinsically less luminous and therefore more normal star-forming galaxies. With this goal in mind, we have conducted a large Herschel survey, the Herschel Lensing Survey, of the cores of almost 600 massive galaxy clusters, where the effects of gravitational lensing are the strongest. In this talk I will discuss how using one of largest gravitational lens enables the detailed study of star forming regions at high redshift by investigating a giant (D ~ 1 kpc) star forming region in a DSFG at z=0.6. Next, I will discuss how using one of the brightest sources from our sample allows us to investigate the molecular gas and dust properties of a typical DSFG at z~2. Finally, I will discuss ongoing work using the brightest DSFGs in our sample to detect rest-frame optical nebular emission lines, which will help characterize their physical properties, such as dust attenuation and metallicity.

February 17, 2016

 "Better living through computation: Exploring the first generations of galaxies
with cosmological simulations"

Brian O'Shea
Michigan State University

 Galaxies are complicated beasts - many physical processes operate simultaneously, and over a huge range of scales in space and time. As a result, accurately modeling the formation and evolution of galaxies over the lifetime of the universe presents tremendous technical challenges. In this talk I will discuss these challenges and their solutions, and will also present results from the Renaissance Simulations - a suite of physics-rich simulations of high redshift galaxy formation done on the Blue Waters supercomputer. These calculations, which include radiation transport and a wide variety of other physical effects, resolve virtually every halo that may possibly form stars and make a variety of predictions about the transition to metal-enriched star formation, the bulk properties of high-redshift galaxies, and the high-redshift luminosity function.

February 24, 2016

 "PHAT Star Clusters: Insights on Star & Cluster Formation from M31"

Cliff Johnson
Postdoctoral Scholar

 The clustering of newly formed stars results from a combination of complex physical processes. Long-lived star clusters represent valuable tracers of star formation physics (gas collapse and feedback), providing constraints on the characteristics and intensity of past star formation. We perform an unparalleled census of M31 star clusters using data from the Panchromatic Hubble Andromeda Treasury (PHAT) survey, producing a well-characterized catalog of >2700 clusters. Combining cluster constraints with measurements of M31's star formation history and ISM, I examine systematic variations in star cluster formation efficiency and the star cluster mass function as a function of star formation rate surface density and gas depletion time. Building from recent theoretical modeling efforts, I explore how observations of cluster formation inform our understanding of star formation and stellar feedback.

March 2, 2016

 "Nuclear Gas Dynamics in Luminous Infrared Galaxies"

Vivian U
UC Chancellor's Postdoctoral Fellow
UC Riverside

 Gas-rich galaxy mergers provide a means to funnel gas into the central region of the system, consequently triggering episodes of nuclear star formation and supermassive black holes growth. The details of the fueling and feedback are often obscured by the cocooning dust stirred up from the violent interaction. To probe the small-scale gas kinematics in the inner kiloparsec region of these local luminous infrared galaxies requires high spatial resolution observations of their nuclei. Here I present results from our Keck Adaptive Optics near-infrared integral-field survey of the nuclear regions in late-stage galaxy mergers. Our findings characterized and addressed the nature of nuclear disks, outflows driven by AGN and starbursts, as well as the role of mergers in black hole-galaxy bulge scaling relations. Our observations further enabled several case studies showing direct evidence of biconical molecular outflows as well as shocked gas from winds and ISM collision between progenitor galaxies.

March 4, 2016

NOTE: Special Astro Seminar Today in lieu of Journal Club
(@ Noon in SERF 383 - Pizza provided)
 "Black holes and the multiverse"

Alex Vilenkin
Director, Institute of Cosmology, and L. and J. Bernstein Professor of Evolutionary Science
Tufts University

 Spherical domain walls and vacuum bubbles can spontaneously nucleate and expand during the inflationary epoch in the early universe. After inflation ends, the walls and/or bubbles form black holes with a wide spectrum of masses. For some parameter values, the black holes can serve as dark matter or as seeds for supermassive black holes at galactic centers. This mechanism of black hole formation is very generic and has important implications for the global structure of the universe. Black holes with mass greater than certain critical value contain inflating universes inside. The resulting multiverse has a very nontrivial spacetime structure, with a multitude of eternally inflating regions connected by wormholes.

March 9, 2016

 "Introduction to Gravitational Wave Physics and Astrophysics with the
Advanced LIGO Detectors"

Alan Weinstein

 We will give an overview of the physics and astrophysics of gravitational waves, with emphasis on sources accessible to the LIGO detectors, as well as an overview of the detectors themselves. Results from the first Advanced LIGO observing run will be mentioned, with more details in tomorrow's Physics Colloquium.

March 11, 2016

NOTE: Special Astro Seminar Today in lieu of Journal Club
(@ Noon in SERF 383 - Pizza provided)
 "Investigating the Possibility of Engineering Bionic Plants"

Eddie C. Red
Assistant Professor, Department of Physics
Morehouse College

 Research conducted in the Research Experience with Diversity (R.E.D.) Laboratory at Morehouse College is focused on three broad categories: Atomic, Molecular, & Optical (AMO) Physics – both computational and experimental; Materials Science Physics; and Nuclear Physics. AMO research projects are centered on studying the dynamics governing electronic processes associated with low kinetic energy photo-ionized charged particles. Research projects include an experimental component that is married with a computational calculation for verification of results. Projects in Materials Science Physics are focused on the growth and characterization of pure- and doped- metal oxide nanotube arrays, which have applications in solar cell technology, batteries, and sensors. Lastly, projects pursued in the area of Nuclear Physics are geared towards developing techniques & materials that will aid in nuclear nonproliferation and remote detection. In addition, projects also include the characterization of materials suitable for use in Light Water Reactors (LWR).

March 16, 2016

NOTE: Kyoto Prize Lecture @ 3:30 PM - Price Center West Ballroom
(No Astro Seminar Today)

Michel Mayor, speaker/recipient
Professor Emeritus of Astronomy
University of Geneva

 World-renowned astrophysicist Michel Mayor, Ph.D., will speak at UCSD on March 16 at 3:30 p.m., as part of the annual Kyoto Prize Symposium. To attend the free talk, which is open to the public, please click here. Read UCSD News story here.

March 18, 2016

NOTE: Special Astro Seminar Today in lieu of Journal Club
(@ Noon in SERF 383 - Pizza provided)
 "Doppler spectroscopy: A path to the detection of Earth-twins hosted by
nearby solar-type stars?"

Michel Mayor, recipient of Kyoto Prize 2015
Professor Emeritus of Astronomy
University of Geneva

 Space missions are the most succesful to detect rocky planets . Nevertheless if we want to detect very low mass planets hosted by nearby ( < 30 pcs ) solar-type stars, the Doppler spectroscopy remains the most promising technique. However due to the intrinsic variability of stellar atmospheres, it is challenging with that technique to detect Earth-twins in the habitable zone. Thanks to the angular separation between these planets and their host star as well as their luminosity these planetary systems could be important targets for future studies.

As the habitable zone is much closer to low mass stars than solar mass stars, the search of potentially habitable rocky planets hosted by M dwarfs is preferred by most of the current surveys looking for transiting planets or by Doppler spectroscopy. However we are not certain if M dwarf stars do not have possible drawback for life development. In the future, some space experiments like TPF or Darwin interferometers adapted to search for biomarkers in the atmospheres of solar analogues could be reconsidered . It is maybe useful to explore the possibilities (and difficulties) to detect rocky planets in the HZ of nearby solar-type stars.

Spring 2016

March 30, 2016

 “Disentangling The Pathways to Co-Evolution of Supermassive Black Holes
and Galaxies”

Brooke Simmons
Einstein Postdoc Fellow

 Supermassive black holes and AGN co-evolve over cosmic time, but despite more than a decade of research the engine(s) for this co-evolution are still not fully understood. The typical co-evolution picture invokes major galaxy mergers to both drive material toward the centre of the gravitational potential and trigger star formation, growing both galaxy and black hole together. This is certainly a plausible explanation for many observed systems, but there is growing evidence from both local ground-based and higher-redshift HST observations that supermassive black holes often grow in systems that cannot have had a major merger. This talk will review the field of black hole-galaxy co-evolution from 0 < z < 3 and across many orders of magnitude in the AGN luminosity and black hole mass function, and discuss the relative importance of both mergers and completely calm, "secular" evolution on black hole growth. New evidence from recent years suggests merger-free process may contribute significantly to both the overall growth of supermassive black holes and their co-evolution with their host galaxies.

April 6, 2016

 "Spiral Structure in Galaxies"

Jerry Sellwood

 Recurrent spiral patterns in galaxy disks redistribute angular momentum, increase random motions, cause radial mixing, smooth rotation curves, amplify the magnetic field, etc. Some spirals are clearly tidal in origin and others may be driven by bars, but other mechanisms seem required to account for their ubiquity. I will present a general assessment of our understanding of the origin of self-excited spiral patterns in galaxies, with a strong focus on the nature of the transient patterns in simulations. The picture that seems to be emerging is that the spiral patterns are true instabilities of a non-smooth disk, and the saturation and decay of one instability seeds the growth of another. Future ground- and space-based surveys to measure the kinematics and chemistry of stars across the Milky Way will yield data that could confirm or refute this idea.

April 12, 2016

NOTE: Special Astro Seminar Today (@ 4:00 in SERF 383)
 "The Euclid challenge"

Eduardo Martín
CSIC Research Professor
Centre for Astrobiologia

 Euclid is a 1.2-meter wide field space telescope designed to measure accurately the expansion history of the Universe and the growth of cosmic structures.

Starting in 2021, it will carry out an optical and near-infrared imaging sky survey, as well as a near-infrared spectroscopic survey. Euclid will cover 15,000 sq. deg., roughly one third of the entire sky, during 6 years.

The unprecedented measurements will address fundamental questions about dark energy, gravity, dark matter, and the initial parameters in the Universe. Euclid was adopted as a Medium Class mission by the European Space Agency (ESA)in 2012. In 2013 NASA became a partner in the Euclid mission.

The Euclid Science Team (EST) is an advisory body to ESA regarding the scientific objectives and implementation of the mission.

Prof. Martin is an ESA-appointed independent legacy scientist in the EST. He leads an international team of scientists focusing on (sub)stellar science with Euclid. In this presentation Martin will talk about the current challenges facing Euclid, as well as the plans to carry out legacy science on stars, brown dwarfs and exoplanets using this unprecedented space-based wide survey.

April 13, 2016

 "Reverberation mapping as a probe of black hole masses and AGN structure: new results from intensive monitoring campaigns"

Aaron Barth
UC Irvine

 The method of reverberation mapping uses the time delay between continuum and emission-line variations in active galactic nuclei to probe the structure of the broad-line region and to derive estimates of black hole masses. Reverberation mapping results provide a fundamental low-redshift calibration for the methods used to trace the cosmological evolution of supermassive black holes. I will present recent developments in reverberation mapping based on observations from the Lick AGN Monitoring Project and from the AGN-STORM project, which carried out a 6-month intensive program of monitoring the nearby Seyfert 1 galaxy NGC 5548 in 2014.

May 4, 2016

 "Modeling merging black holes with numerical relativity in the era of first
gravitational-wave observations"

Geoffrey Lovelace
Assistant Professor, Department of Physics
Cal State University, Fullerton

 Advanced LIGO has made the first observation (named GW150914) of gravitational waves passing through Earth. This gravitational-wave signal originated from merging black holes, one of Advanced LIGO's most promising sources. Near the time of merger, the emitted gravitational waves from colliding black holes can only be computed using numerical relativity. In this talk, I will present new numerical-relativity simulations of merging black holes, made using the Spectral Einstein Code. Specifically, I will present new gravitational waveforms, including those from merging black holes with spins nearly as fast as possible, an especially challenging but potentially astrophysically important case. I will also discuss how these and other simulations of merging black holes enable rapid follow-up of gravitational-wave observations, including GW150914, helping to maximize our understanding of the observations' sources.

May 11, 2016

 "Dusting for Prints of Exoplanetary Systems"

Christine Chen
Associate Astronomer
Space Telescope Science Institute (STScI)

 Debris disks are dusty disks around main sequence stars that are distinguished from proto-planetary disks by their small gas:dust ratios. Without bulk gas to retard the loss of particles against radiation pressure or corpuscular stellar wind and Poynting-Robertson (CPR) drag, circumstellar grains typically possess lifetimes of <10,000 years, significantly shorter than the age of the central star, implying that the grains are replenished from a reservoir. In these systems, unseen planets are presumed to perturb minor bodies such as asteroids or comets into crossing orbits, generating small dust grains that are detected via remote sensing. The Spitzer Space Telescope enabled the discovery and characterization of more than one thousand debris disks for the first time. I will (1) provide an overview of debris disks as planetary systems, (2) describe the time and mass dependent evolution of the mid- to far-infrared properties of debris disks and (3) describe how debris disk properties can be used to constrain the architecture of underlying planetary systems. I will also describe outstanding questions about debris disk evolution that will be addressed using the next generation of ground- and space-based instruments.

May 12, 2016

NOTE: Special Astro Seminar Thursday @ Noon in SERF 329
(Pizza will be provided)
 "What N-PDFs tell us about the processes of molecular cloud
and star formation"

Nicola Schneider
I. Physik. Institut,University of Cologne, Germany

 Hydrogen column density maps of molecular clouds are one of the most important observables in the context of molecular cloud- and star-formation studies. They reflect the structure of the ISM and constitute the gas reservoir out of which stars form. The Herschel photometric maps (70-500 micron) allow now to determine column density maps over a very large dynamic range.

Our group of observers and theorists specialized in the last years on the interpretation of probability distribution functions (N-PDFs) of column density. N-PDFs are used to evaluate the relative importance of gravity, turbulence, magnetic fields, geometry, and radiative feedback governing the cloud's density structure and star-formation activity. I will present a selection of our most important results:

1. For a proper interpretation of N-PDFs, line-of-sight contamination, completeness limits, and resolution effects need to be considered.

2. We found clear indications that the power-law tail commonly found in N-PDFs is caused by self-gravity of filaments and clumps, and free-fall collapse of cores.

3. Infrared dark clouds reveal a power-law tail and are thus dominated by gravity, and not turbulence, even at an early evolutionary state.

4. The most massive giant molecular clouds show an additional power-law tail with flatter slope at the highest column densities, indicating a slowed-down collapse.

5. N-PDFs combined with PDFs from HI observations allow to trace precisely the HI/H2 transition in the ISM.

6. The N-PDFs of high-density molecular line tracers such as N2H+ and CS show a power-law tail that corresponds to the one from dust. However, abundance variations and different regimes of excitation limit the functionality of molecular line PDFs.

May 13, 2016

NOTE: Special Astro Seminar Today in lieu of Journal Club
(@ Noon in SERF 383 - Pizza provided)
 "Planck, BICEP, and the Early Universe"

Raphael Flauger
Assistant Professor, Department of Physics
University of Texas at Austin

 The cosmic microwave background contains a wealth of information about cosmology as well as high energy physics. It tells us about the composition and geometry of the universe, the properties of neutrinos, dark matter, and even the conditions in our universe long before the cosmic microwave background was emitted. After a brief introduction, I will discuss various aspects of the recently released Planck full mission data before turning to a discussion of string inspired models and the search for their signatures. Finally, I will turn to the search for primordial B-modes.

May 18, 2016

 "Exoplanet Climatology: The Next Era of Habitable-planet Hunting"

Aomawa Shields
NSF Astronomy and Astrophysics Postdoctoral Fellow and UC President's Postdoctoral Program Fellow
UCLA and Harvard-Smithsonian CfA

 The identification of an exoplanet receiving the amount of incident radiation from its host star to lie within the star’s habitable zone has been the primary step taken in classifying a planet as "potentially habitable". However, recent research and the history of our own planet have shown that many factors and processes can affect climate and planetary habitability. Discovering a planet in the habitable or "Goldilocks" zone is therefore but a first step in the process of finding the next planet where life can survive. To identify habitable worlds beyond our solar system, it is important to understand how both orbital and atmospheric properties affect the climate of exoplanets, and how these climatic effects might change for different stellar and planetary environments. I will share results from work performed using a hierarchy of models to simulate planets orbiting stars of different spectral types and with varied orbital architectures, and discuss the implications of these results for planetary climate and habitability. This work ushers in a new era of utilizing observational data and theoretical techniques together to target the next planet where life might exist.

May 25, 2016

NOTE: Hans E. Suess Memorial Lecture @ 4:00 in NSB Auditorium

                              -- Reception from 3:00-4:00 in NSB Atrium --
                                      (Today's talk is in lieu of the Astro Seminar)

 "The Chemistry of planet formation"

Karin Öberg
Professor of Astronomy

 During the past decade, the number of known exoplanets has increased explosively, revealing an extreme range in planet compositions. Some of the detected planets are theorized to be ‘habitable’, i.e. of the right temperature and bulk composition. This raises two important questions, what processes set the bulk compositions of planets, and how often are ‘habitable’ planets actually chemically habitable, i.e. rich in water and organic material. Both questions are intimately linked to the composition of gas and solids that planets assemble from in protoplanetary disks, and especially to the processes that regulate ice build-up, chemical evolution, and sublimation. To address these questions, we use spatially and spectrally resolved observations to map out the distributions of bulk and trace volatiles in protoplanetary disks. Recent highlights include observations of spectacular ring structures that trace condensation fronts in disks, new constraints on isotopic fractionation in volatiles during planet formation, and detections of complex organic molecules in disks. Several of these observations were surprises that have inspired new theoretical developments and new laboratory experiments on ice chemistry. I will present on how these new observations, models and experiments together have informed our understanding of how chemistry regulates key aspects of planet formation.

June 1, 2016

 "Searches for dark forces"

Susan Gardner
Professor of Physics & Astronomy
University of Kentucky / UC Irvine

Summer 2016

June 15, 2016

NOTE: Special Astro Seminar Today @ Noon in SERF 329
 “X-rays across the galaxy population: tracing star formation and AGN activity”

James Aird
Cambridge University

 I will present new work that combines large samples of galaxies from the CANDELS and UltraVISTA surveys with deep Chandra data to measure the distribution of X-ray luminosities across the galaxy population. Our measurements allow us to trace two origins of the X-ray emission: star formation and AGN activity.

At low luminosities, we identify narrow peaks that we associate with star formation processes (tracing the combined emission from X-ray binaries throughout the galaxy). By tracking the position of these peaks as a function of stellar mass and redshift we provide new, independent measurements of the galaxy "star-forming main sequence", based on the X-ray emission. We measure a star-forming main sequence with constant slope of ~0.8, a normalization that evolves strongly with redshift, and no evidence for a turn-over or flattening at high stellar masses.

We also identify a tail in our distributions to higher X-ray luminosities that allows us to trace AGN activity. We use these data to measure the distribution of AGN accretion rates in both star-forming and quiescent galaxies, as a function of stellar mass and redshift. Our results reveal a broad distribution of accretion rates in both galaxy types, reflecting the stochastic nature of AGN triggering and fuelling. We also find that the incidence of AGN in star-forming galaxies is higher than in quiescent galaxies and undergoes a strong, stellar-mass-dependent evolution. The probability of a quiescent galaxy hosting an AGN is generally lower but does not depend on stellar mass and evolves differently with redshift. These results provide vital insights into the physical mechanisms that drive the growth of supermassive black holes and reveal the relationship between AGN and their host galaxies.