List of Past Astronomy Colloquia : 01-Sep-2022 to 31-Dec-2022

Date:   Wednesday 07-Sep-2022
Speaker:   Dr. James Jackson (NRAO)
Title:  The Radio Ammonia Mid-Plane Survey (RAMPS)

The Radio Ammonia Mid-Plane Survey used the K-band Focal Plane Array on the 100-m Green Bank Telescope to map the NH3 (1,1) through (5,5) inversion lines and H2O maser emission over 21.6 square degrees in the first quadrant of the Galactic Plane. The survey identified 2,680 dense molecular clumps in various evolutionary stages, from pre-stellar, to protostellar, to H II regions. A virial analysis of the clumps shows that the majority of clumps are unstable to gravitational collapse. Over 80% of pre-stellar and protostellar clumps have virial parameters < 0.5. The ensemble also shows kinematic evidence for collapse via the "blue” asymmetry of an optically thick tracer (13CO) with respect to an optically thin tracer (NH3). These clouds are so opaque that even 13CO is optically thick (typically tau~5). Finally, RAMPS data reveal unusual NH3 emission from the filamentary Infrared Dark Cloud G23.33-0.30. Toward this source, the NH3 linewidths are unusually broad (~25 km/s) and the NH3 (3,3) line reveals unusual maser emission. Follow up observations with the VLA and SMA indicate that this cloud is being struck by a supernova blast, which has heated, accelerated, and injected turbulence into a portion of the filament.

Date:   Wednesday 14-Sep-2022
Speaker:   Dr. Jane Rigby (GSFC)
Title:  Commissioning JWST + early science

JWST is a large (6.5m diameter), cold (<50 K) infrared-optimized astronomical observatory with a segmented mirror design, which was launched on 25 Dec. 2021, unfolded in space, and entered science operations in July 2022. Commissioning has demonstrated that JWST is fully capable of achieving the discoveries for which it was built. Almost across the board, the science performance of JWST is better than expected: the images are sharper, the pointing is more stable and precise, and the science instruments have generally higher total throughput than pre-launch expectations. Collectively, these factors translate into better sensitivity than assumed before launch, in many cases by tens of percent. As one of the three commissioning scientists for JWST, the speaker was deeply involved in all aspects of commissioning the spacecraft, telescope, and science instruments. The speaker is also the PI of the JWST Early Release Science program TEMPLATES, which is studying star formation in galaxies that have been gravitationally lensed. This talk will provide behind-the-scenes stories of commissioning the world's most powerful space observatory, summarize the currently-known science performance of JWST, and highlight early science that is emerging, with a look ahead.

Date:   Wednesday 21-Sep-2022
Speaker:   Violeta Gamez Rosas (Leiden)
Title:  Resolving the dusty heart of NGC 1068 with MATISSE

In the Unification Theory of AGNs the concept of "the torus" plays a crucial role to discern between Type-1 and Type-2 AGNs. Its emission, coming from hot and warm dust peaks at infrared wavelengths, which makes MATISSE an ideal instrument to observe it. The wide spectral coverage of the L, M and N bands, and the high spatial resolution that MATISSE offers, together with its capability to combine the beams of four telescopes to do interferometry, therefore generating closure phases, make the instrument a versatile tool for the study of AGNs. NGC 1068, being one of the closest AGNs, has been considered a key science case for MATISSE. In this talk I will present the first image reconstructions of the dusty heart of NGC 1068, and the thermal and extinction map derived through Gaussian modelling and aperture photometry. By cross-identifying this map with ALMA and VLBA maps and the water masers, we can determine the position of the super massive black hole. This analysis unveils an optically thick ring that is obscuring the central engine at parsec scales and a less optically thick disk extending to at least 10 pc. We find a striking similarity between the morphologies of the radio free-free emission and the thermal emission of the dust in both, the L and N bands. We also find that the cold obscuring dust is mainly formed by amorphous olivines and carbon grains.

Date:   Wednesday 28-Sep-2022
Speaker:   Yuhan Yao (Caltech)
Title:  Tidal Disruption Events: Probes of Accretion Physics and Black Hole Demographics

Fundamental open questions about black holes (BHs) remain in astrophysics. For example, there is a dearth of information about the existence and demographics of intermediate-mass BHs (IMBHs), and BH super-Eddington accretion is observationally poorly characterized. Over the past few years, time domain sky surveys such as the Zwicky Transient Facility (ZTF) optical camera and the Spektrum-Roentgen-Gamma X-ray satellite have led to a resurgence of tidal disruption event (TDE) discoveries in galaxy centers. In this talk, I will present observational advances of TDEs across the electromagnetic spectrum and with multiple messengers. I will highlight how detailed studies of two ZTF-discovered TDEs (AT2021ehb and AT2022cmc) have helped us understand the inflow geometry and relativistic outflow launching under super-Eddington accretion. The era of TDE studies will continue to be exuberant as the Vera C. Rubin Observatory LSST survey comes online in 2023. I will describe the opportunities and challenges in inferring the local BH mass function down to the IMBH regime with future TDE sample studies.

Date:   Wednesday 05-Oct-2022
Speaker:   Dr. George Younes (GSFC)
Title:  Magnetars: a cosmic physics lab

Magnetars form a sub-population within the isolated neutron star zoo, occupying a unique parameter space in the famed p-pdot diagram. Assuming magnetic dipole radiation, their inferred magnetic fields are on average two orders of magnitude larger than regular pulsars. This immense reservoir of magnetic energy fuels their bright persistent surface thermal, and magnetospheric non-thermal X-ray emission. It is also the driver of sub-second soft gamma-ray flashes, giant flares (brightest X-ray events detected, after the sun), and years-long outbursts during which extreme variability is observed; altered spectral and pulse shapes, glitching activity, strong timing noise, appearance of radio activity, among other attributes. All the above relate to the dynamic internal structure of these sources, the way in which that impacts the exterior through twisted field lines, and the influence of the high B-field on the observed electromagnetic radiation. Additionally, the large energy stock of magnetars is commonly invoked as a power source for other extreme transient phenomena, such as gamma-ray bursts, superluminous supernovae, ultra-luminous X-ray sources, and finally fast radio bursts (FRBs). Smoking-gun evidence for the latter occurred on 2020 April 28, when an FRB-like radio burst was simultaneously detected with an X-ray burst from the Galactic magnetar SGR 1935+2143. In this talk, I will summarize the latest high energy observational results from a few Galactic magnetars, their relation to FRBs and other extragalactic phenomena, and their strength in providing great insight into neutron star physics and radiative processes in high B-field regime.

Date:   Wednesday 12-Oct-2022
Speaker:   Dr. Adi Foord (Stanford/Kavil)
Title:  Searching for Dual AGN: A Unique Flag of Merger-Driven SMBH Growth

After decades of SMBH observations, the connection between AGN triggering and galaxy mergers remains incomplete, although AGN are likely key players in the evolution of massive galaxies. Theoretically, there are many reasons to expect a link between galaxy mergers and the accretion of material onto at least one of the central supermassive black holes. Yet, observationally, varied results have led to uncertainty in whether AGN triggering is dependent on environment. One of the best ways to analyze the possible ties between merger environments and SMBH activity is to study systems with unique observational flags of merger-driven SMBH growth -- or, dual AGN. I will present my work quantifying the dual AGN fraction at both high redshifts, and as a function of redshift, via a large and uniform study of dual AGN in X-rays, up to z=3.5. By analyzing available data in wide and deep public Chandra surveys, the dual AGN fraction at both the high-redshift (2.5 < z < 3.5) and low-redshift (z < 0.03) regime can be better constrained. Pairing X-ray results with available multi-wavelength data, we gain insight on how the X-ray activity of interacting AGN depends on their environments. Lastly, I will highlight the capabilities of future high spatial-resolution X-ray observatories, which will revolutionize the field of dual AGN detectability, and our understanding of the role mergers play in AGN triggering.

Date:   Wednesday 19-Oct-2022
Speaker:   Dr. Shriharsh Tendulkar (Tata Institute)
Title:  Multi-messenger and multi-wavelength observations of Fast Radio Bursts

Fulfilling the true promise of fast radio bursts (FRBs) as cosmological probes, understanding their origins, and their association with other transients ecessitates our understanding of the FRB emission mechanism, their formation channel(s), and their local environments. Most emission mechanisms expect that the prompt radio emission represents a small fraction of the total energy released — a larger fraction of the energy should be released at higher frequency wavebands: optical, UV, X-ray and in some cases, gravitational waves (GW) and neutrinos, either as prompt emission or as a longer-lived afterglow. Given that the observed rates of FRBs are two to three orders of magnitude higher than the sky rates of any other extragalactic transient, it is clear that most FRBs will not have detectable multi-wavelength counterparts. The X-ray bursts aligned with the FRB-like radio emission from SGR 1935+2154 highlight the need to be alert to the brightest and nearest FRBs since those will be the most likely to have detectable multi-wavelength counterparts. In this talk I will discuss results from CHIME/FRB in trying to constrain counterparts of FRBs, FRB-GRB connections, and FRB-GW connections. For these science cases, I will also discuss two upcoming projects: The proposed All Sky Transient Radio Array (ASTRA), an ultra-wide field of view telescope to detect the brightest and nearest radio transients and Daksha, a proposed all-sky X-ray mission with 2-satellites in antipodal orbits to increase the detection rate of GRBs and electromagnetic counterparts of GW events.

Date:   Wednesday 26-Oct-2022
Speaker:   Dr. Jacob Bean (University of Chicago)
Title:  Dawn of the JWST Exoplanet Era

JWST commenced science operations in July and is producing a torrent of exquisite data for transiting exoplanets. I will give a summary of the findings that have come out of these first observations, with a focus on the results from the community Early Release Science Program. As of this writing we have published the first detection of CO2 in an exoplanet atmosphere, and further transformative discoveries are already in hand.

Date:   Wednesday 02-Nov-2022
Speaker:   Dr. Daniella DellaGiustina (University of Arizona)
Title:  OSIRIS-APEX: An OSIRIS-REx Extended Mission to Asteroid Apophis

The Origins, Spectral Interpretation, Resource Identification, and Security-Regolith Explorer (OSIRIS-REx) spacecraft mission characterized and collected a sample from asteroid (101955) Bennu. After the OSIRIS-REx Sample Return Capsule is released to Earth's surface in 2023, the spacecraft will divert into a new orbit that encounters asteroid (99942) Apophis in 2029, enabling a second mission with the same unique capabilities: OSIRIS–Apophis Explorer (APEX). On April 13, 2029, the 340-m-diameter Apophis flies within ~32,000 km of Earth's surface, <1/10th the lunar distance. Apophis will be the largest object to approach Earth this closely in recorded history. This rare planetary encounter will alter Apophis' orbit, subject it to tidal forces that change its spin state and may seismically disturb its surface. APEX will distantly observe Apophis during its Earth encounter and capture its evolution in real-time, revealing the consequences of an asteroid undergoing tidal disturbance by a major planet. The spacecraft's instrument suite will subsequently provide high-resolution data of a "stony" asteroid—advancing knowledge of these objects and their connection to meteorites. Near the mission's end, APEX will perform Regolith Excavation by S/C Thrusters; a technique demonstrated at Bennu. Observations during and after excavation will provide insight into the material properties of stony asteroids. Furthermore, Apophis' material and structure have critical implications for planetary defense.

Date:   Wednesday 09-Nov-2022
Speaker:   Dr. Wendy Freedman (University of Chicago)
Title:  "The Hubble Tension: Is There a Crisis in Cosmology?"

An important and unresolved question in cosmology today is whether there is new physics that is missing from our current standard Lambda Cold Dark Matter (LCDM) model. Recent measurements of the Hubble constant (Ho), which are based on Cepheids and Type Ia supernovae (SNe), appear to be discrepant at the 5-sigma level with values of Ho inferred from measurements of fluctuations in the cosmic microwave background (CMB). If real, the current discrepancy could be signaling a new physical property of the universe. I will present results based on Hubble Space Telescope Advanced Camera for Surveys data resulting in an independent calibration of SNe Ho based on measurements of the Tip of the Red Giant Branch (TRGB). The TRGB marks the luminosity at which the core helium flash in low-mass stars occurs, and provides a high-precision and accuracy standard candle. Moreover, the TRGB method is less susceptible to extinction by dust, to metallicity effects, and to crowding/blending effects than Cepheid variable stars. I will address the current uncertainties in both the TRGB and Cepheid distance scales, as well as discuss the current tension in Ho and the evidence for additional physics beyond the standard LCDM model.

Date:   Wednesday 16-Nov-2022
Speaker:   Dr. Jason Glenn (GSFC)
Title:  â€śPRIMA: the Probe far-Infrared Mission for Astrophysics”

PRIMA is a far-infrared observatory concept being developed to address timely and fundamental questions about the growths of galaxies and solar systems and their constituents. It will observe the build-up of heavy elements, dust, stars, and black holes in galaxies and their interrelationships, and trace the masses and water contents of protoplanetary disks to probe the growths of solar systems. The majority of observing time will be devoted to Guest Observer programs to enable the astrophysics community to identify and plan the most critical observations, with focused PI programs to address key science with rapid releases of data to inform community planning. PRIMA will have spectral, hyperspectral imaging, and polarimetric capabilities, enabled now for the first time by extraordinary progress in kinetic inductance detector (KID) array technology over the last two decades. The 2-meter telescope will be cooled to < 5 K to take maximum advantage of the KID sensitivities. For observations of atomic fine-structure lines, molecular lines, and solid-state emission and absorption bands, R = 170 spectral coverage will range from approximately 24 microns to 230 microns, with a high-resolution mode across the entire band that will have a spectral resolving power of 4,400 at 112 microns. R ~ 10 moderate-resolution (hyperspectral) imaging will range from 25 to 80 microns for rest-frame mid- and far-infrared spectral energy distribution measurements to probe dust grain composition and disambiguate star formation and active galactic nuclei in galaxies. Polarimetric observations of large areas of Galactic molecular clouds and the Magellanic Clouds from 80 to ~200 microns will bridge between the large-scale polarimetry of the interstellar medium from cosmic microwave background observatories and protostellar disk-scale interferometric observations to probe magnetic fields at the critical scales at which clouds collapse to form stars. An overview of PRIMA’s basic design and capabilities will be presented.

Date:   Wednesday 23-Nov-2022

Date:   Wednesday 30-Nov-2022
Speaker:   Dr. Martin Turbet (LMD/IPSL)
Title:  The Generic Planetary Climate Model, one model to simulate them all

The Generic Planetary Climate Model or "Generic PCM" is a community code, historically developed in France at the Laboratoire de Météorologie Dynamique (LMD), aimed at simulating in 3D the atmosphere of all types of planets.

The model already has numerous applications: studying atmospheric dynamics on Jupiter, Saturn and the icy giants, simulating the interaction between the atmosphere and ices on Pluto and Triton, the hazes and photochemistry n Titan, the paleoclimates of Mars, Earth and Venus, exploring the climates of exoplanets, from the coldest and smallest to the largest and hottest, and link them to astronomical observations.

After giving you a brief overview of the model, of its main components and specificities, I will present you a panorama of recent applications, with a focus on telluric planets and exoplanets.

Date:   Wednesday 07-Dec-2022
Speaker:   Dr. Mark Vogelsberger (MIT)
Title:  Simulating Early Structure and Galaxy Formation - The THESAN Project

Cosmological simulations of galaxy formation have evolved significantly over the last decade. In my talk I will describe recent efforts to model the large-scale distribution of galaxies with cosmological hydrodynamical simulations. The focus of the talk will be a discussion of our new simulation campaign, the THESAN project, to study the epoch of reionization and the early Universe.

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