List of Past Astronomy Colloquia : 01-Sep-2016 to 31-Dec-2016

Date:   Wednesday 07-Sep-2016
Speaker:   Dr. Michael Fall (STScI)
Title:  Formation of the Hubble Sequence

This talk explains the formation of galaxies of different morphological types (aka the Hubble Sequence): spirals vs ellipticals, disks vs spheroids. The talk includes theory, observation, and simulation, and is aimed at a general astrophysics audience. Some highlights of the talk are the following: (1) The morphologies of galaxies are closely related to their specific angular momenta. (2) Disk-dominated galaxies have about the same specific angular momenta as their dark-matter halos; spheroid-dominated galaxies have about five times less. (3) Feedback by young stars (stellar radiation and winds, supernovae, etc) and active galactic nuclei is crucial for understanding the angular momenta of galaxies and hence their morphologies and hence the Hubble sequence. (4) The relations between the specific angular momenta and sizes of galaxies and their halos are nearly constant over the redshift range 0 < z < 3; galaxies and halos grow together nearly homologously.

Date:   Wednesday 14-Sep-2016
Speaker:   Dr. Alexandra Pope (UMASS)
Title:  Dust-obscured star formation at the Cosmic Frontier: New observations from the Large Millimeter Telescope

While UV surveys have mapped out the unobscured star formation rate density over cosmic time, our observations of obscured star formation remain incomplete beyond z~3. Millimeter observations are crucial to complete the census of star formation in the Universe. I will present new observations with the Large Millimeter Telescope including a 1.1 mm survey of the HST Frontier Fields. The clusters act as cosmic telescopes to amplify lower-luminosity galaxies, probing further down the millimeter luminosity function than possible with blank-field observations. With this survey we detect dust in galaxies with star formation rates as low as ~10 solar masses per year allowing us to measure the dust-obscured star formation in typical galaxies in the distant Universe. I will discuss the synergy between the wide surveys with the LMT and targeted programs with ALMA.

Date:   Wednesday 21-Sep-2016
Speaker:   Dr. Joel Parriott (AAS)
Title:  Astro Politics & Funding at a Time of Transitions (And I Donít Mean the Atomic Variety)

Since the federal government is the primary source of support for research in astronomy, every member of our community needs to know what is going on in Washington and what they can do about it. This talk will cover the policy and political context for R&D at the federal level, relevant current events, and prospects for the future.

Date:   Wednesday 28-Sep-2016
Speaker:   Dr. Harry Ferguson (STScI)
Title:  CANDELS: Observing Galaxy Assembly

The Cosmic Assembly Near-IR Deep Extragalactic Legacy Survey (CANDELS) is the largest single observing program undertaken with the Hubble space telescope. The Hubble observations are supplemented by the deepest data from X-ray to radio frequencies, with the ain of documenting the the first third of galactic evolution, from redshift z~8 to 1.5. The survey was also designed to find and measure Type Ia SNe beyond z > 1.5 and test their accuracy as standard candles for cosmology. This talk will summarize the findings from the survey, highlighting both emerging insights on the physics of galaxy evolution as well as the open questions that will motivate observations from the James Webb Space Telescope.

Date:   Wednesday 05-Oct-2016
Speaker:   Dr. Jordan Goodman (HAWC-UMD-PHYSICS)
Title:  A New Look at the TeV Sky with the HAWC Gamma Ray Observatory

The High Altitude Water Cherenkov (HAWC) Gamma-ray Observatory in the high mountains of Mexico was completed in March of 2015 and is now giving us a new view of the TeV sky. HAWC is 15 times more sensitive than the previous generation of wide-field EAS gamma-ray instruments and is able to detect the Crab nebula at >5s with each daily transit. In our first year of operation, HAWC has a 5s detection sensitivity for a source of ~50mCrab. Unlike Imaging Atmospheric Cherenkov Telescopes (IACTs), HAWC operates 24hrs/day with over a 95% on-time and observes the entire o verhead sky (~2sr). HAWCís peak energy sensitivity is 2-10 TeV which is ~10x higher than IACTs such as VERITAS and HESS, which makes their observations quite complementary. This talk will present results from the first HAWC catalog including our study of the galactic plane showing more than a dozen new sources not yet detected by IACTs as well as spectra and morphology of bright sources. In addition, results of our monitoring of transient AGN will be presented.

Date:   Wednesday 12-Oct-2016
Speaker:   Dr. Laura Blecha, Dr. Brian Morsony, & Dr. Nathan Roth (UMD)
Title:  See abstracts

Laura Blecha (JSI Prize Fellow, University of Maryland) "Uncovering the Signatures of Obscured AGN in Mergers" Galaxy mergers have long been implicated as key drivers of supermassive black hole (BH) and galaxy co-evolution, but the relative importance of mergers for BH fueling is still a matter of active debate. Observational studies of the connection between mergers and active galactic nuclei (AGN) are heavily influenced by selection effects; in particular, there is evidence that the most luminous AGN are preferentially obscured by dust in late-stage mergers. Infrared (IR) and hard X-ray selected AGN, which are less sensitive to dust obscuration, are significantly more likely to be found in mergers than AGN selected at other wavelengths. I'll describe recent results using numerical simulations with radiative transfer to model the evolution of mid-IR AGN signatures throughout galaxy mergers. I will discuss the efficacy of various mid-IR color selection techniques for identifying single and dual AGN, as well as the potential for the James Webb Space Telescope to reveal spatially-resolved signatures of some of the most rapidly-accreting BHs in the nearby Universe.

Brian Morsony (TCAN Fellow, University of Maryland) "Modeling short GRBs off-axis: A new hope for finding electromagnetic counterparts of gravitational wave events" Short GRBs are believed to be produced by NS-NS and/or NS-BH mergers. These mergers also produced gravitational waves which will be detected by LIGO and Virgo. However, GW events will only be accompanied by a GRB directed at Earth in a small fraction of events. In most cases, localizing the GW event will rely on finding the off-axis GRB afterglow. Based on properties of observed short GRB jets, we model short GRB afterglows as a function of observer angle, along with possible isotropic emission components.

Nathan Roth (JSI Prize Fellow, University of Maryland) "What sets the line widths in tidal disruption events?" Flares from the tidal disruption of stars by supermassive black holes (TDEs) are providing a new perspective on accretion physics. While their emission can span a wide range of spectral energies, from gamma rays through radio, a large collection of spectral data has now been collected in the optical and near UV. These spectra show a stunning amount of diversity. In addition to variations in the strengths of the lines, the widths can differ by over a factor of five between events, even when a similar mass is inferred for the black hole. In some events the lines mysteriously narrow over time. Many theoretical models predict that stellar material will be launched in an outflow, yet the spectra rarely display the P-Cygni line profiles associated with outflows in other astrophysical objects. In this talk I'll present preliminary results from radiative transfer calculations designed to make sense of these observations.

Date:   Wednesday 19-Oct-2016
Speaker:   Dr. Jeff Newman (University of Pittsburgh)
Title:  The Milky Way in its Extragalactic Context

In recent work, we have produced updated estimates of the star formation rate, stellar mass, and disc scale length of the Milky Way by applying Bayesian mixture-model techniques to the extant literature. We have used the results to select a sample of Milky Way analog (MWA) galaxies from the Sloan Digital Sky Survey (SDSS) whose distributions of stellar mass and star formation rate match the Galactic posteriors. Relying on the Copernican assumption that our Galaxy should not be extraordinary, the colors and luminosities of the MWAs constrain the possible photometric properties of our own Galaxy. This has enabled us to explore the location of the Milky Way on spiral-galaxy scaling relations, including the Tully-Fisher relation (TFR) defined by any of optical luminosity, stellar mass, or baryonic mass and the three-dimensional luminosity-velocity-size (LVS) relation, allowing us to explore how the Milky Way fits in with broader galaxy populations. I will describe these findings and their implications for our understanding of the Milky Way and its population of satellite galaxies.

If time allows, I will also discuss the results of two recent reports (separately commissioned by the National Science Foundation and the US Department of Energy) that have explored what instrumental capabilities and community resources are needed to complement LSST in the next decade. These reports have one recommendation in common: the development of a Southern Spectroscopic Survey Instrument capable of massively-multiplexed wide field spectroscopy on a large-aperture telescope.

Date:   Wednesday 26-Oct-2016
Speaker:   Dr. Hal Weaver (JHUAPL)
Title:  The Exploration of Pluto and the Kuiper Belt by NASA's New Horizons Mission


On 2015 July 14 NASA's New Horizons spacecraft flew 12,500 km above the surface of Pluto revealing a world of remarkable complexity and diversity. A giant basin filled with nitrogen ice dominated the encounter hemisphere and is the site of vigorous ongoing solid state convection that generates glacier-like transport along the surface. Giant mountains of water ice appear to be floating in the nitrogen ice. The periphery of the basin has a wide variety of landforms, including ice flow channels and chaotically arranged blocks of water ice. Extensive sublimation pitting is observed within the nitrogen ice sheet, testifying to active volatile transport. Peculiar bladed terrain to the east of the nitrogen ice sheet appears to be coated by methane ice. Pluto's equatorial region is dominated by an ancient dark red belt of material, probably tholins created either by irradiation of surface ices or by haze precipitation from the atmosphere. Pluto sports a wide variety of surface craters with some terrains dating back approximately 4 billion years while some terrains are geologically young. New Horizons discovered trace hydrocarbons in Pluto's atmosphere, multiple global haze layers, and a surface pressure near 10 microbars. Charon, Pluto's largest moon, displays tectonics, evidence for a heterogeneous crustal composition, and a puzzling giant hood of dark material covering its North Pole. Crater density statistics for Charon's surface give a crater retention age of 4-4.5 Ga, indicating that Charon's geological evolution largely ceased early in its history. All of Pluto's four small moons (Styx, Nix, Kerberos, and Hydra) have high albedos, highly elongated shapes, and are rotating much faster then synchronous with their orbital periods, with rotational poles clustered near the Pluto-Charon orbital plane. The surfaces of Nix and Hydra are coated with nearly pristine crystalline water ice, despite having crater retention ages greater than 4 billion years. The New Horizons spacecraft remains healthy and was targeted toward the flyby of a small (~30-40 km) KBO in late-2015, enabling the study of an object (2014 MU69) in a completely different dynamical class (cold classical) than Pluto, during a Kuiper belt Extended Mission (KEM) phase. In addition to the flyby of 2014 MU69 on 2019-Jan-01, the KEM will also include observations of more than a dozen other KBOs at resolutions and geometries not feasible from Earth, and studies of the heliospheric plasma, neutral hydrogen, and the dust environment out to 50 AU from the Sun.

Date:   Wednesday 02-Nov-2016
Speaker:   Dr. William Moore (Hampton University)
Title:  The Blind Men and the Elephant: Feeling Our Way through the Landscape of Planetary Climate Outcomes

The coupled evolution of a planetís atmosphere and interior drives climate change as well as climate stability, but what are the possible climate outcomes of rocky worlds and how likely are we to find examples of each? An extremely simplified coupled mantle-atmosphere system reveals complex behavior even in the presence of only a few linear feedbacks. What are the relevant parameters that control stability, clemency, and longevity and how can we observe them? Like the blind men who encounter an elephant, we need to find a common framework in which to place our observations of rocky worlds orbiting other stars. I will present the beginning of such a framework based on the dynamics of planetary evolution.

Date:   Wednesday 09-Nov-2016
Speaker:   See Events Calendar

Date:   Wednesday 16-Nov-2016
Speaker:   Dr. Namir Kassim (NRL)
Title:  Bill Ericksonís Legacy: Low Frequency Radio Astronomy in and around the JVLA

After coming to the University of Maryland more than fifty years ago, radio astronomer Bill Erickson emerged as a highly respected pioneer in low frequency radio astronomy. What is less well known is that towards the end of his career, his forward thinking vision helped lay the foundations of a renaissance that is still fueling a resurgence in the field today. Many of Professor Ericksonís innovations took root around the Jansky Very Large Array (JVLA), and continue to flourish, including most recently the VLA Low Band Ionosphere and Transient Experiment ( I will take you on a journey through the development of projects inspired by Bill at the JVLA, together with the science that motivated them.

Date:   Wednesday 23-Nov-2016

Date:   Wednesday 30-Nov-2016
Speaker:   Dr. Shawn Domagal-Goldman (NASA)
Title:  Big Bang to Biosignatures: The LUVOIR Decadal Mission ConceptNashua03060

The Large UV/Optical/IR Surveyor (LUVOIR) is a concept for a highly capable, multi-wavelength observatory with ambitious science goals. This mission would enable a great leap forward in a broad range of astrophysics, from the epoch of reionization, through galaxy formation and evolution, to star and planet formation. LUVOIR also has the major goal of characterizing habitable exoplanets around Sun-like stars and searching them for signs of life.

LUVOIR is one of four Decadal Survey Mission Studies initiated in Jan 2016. The final report will be submitted to NASA and then the National Academies in 2019. Here I will summarize LUVOIRís broad and revolutionary science goals, with a focus on the exoplanet science this telescope would enable. This includes both the focused science associated with the search for biosignatures on potentially habitable worlds, as well as a broad survey of the kinds of worlds in our stellar neighborhood. Both of these areas of science would be vastly advanced by a LUVOIR-like telescope. Iíll close with an explanation of the study process, the instruments and architectures that have been chosen by the STDT, and how that process will feed into the decadal survey.

Date:   Wednesday 07-Dec-2016
Speaker:   Dr. Leslie Sage (University of Maryland)
Title:  How to publish a paper in Nature

Nature is one of the world's leading scientific journals, publishing many papers that receive wide attention by the general public. But, Nature is very selective-- <7% of submitted papers are published. In order to maximize your chances of getting published, papers should present fundamental new physical insights, or startling observations/results. Theory papers pose additional problems, as we want only those papers that are likely to be the correct explanation, and not simply exploring parameter space. The writing should be clear, concise and directed at the level of a graduate course in the subject. I encourage authors to contact me in advance of submission of a paper, both to ascertain the appropriateness of the result for Nature, and to ensure that the writing is close to our standards. Posting to ArXiv is and always has been allowed, but authors should discuss the specifics with their institutional public affairs officers before doing so. Lapses in professional ethics seem to be on the rise Ė I will discuss some examples, and what we should be doing to keep astronomy clean.

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