Remote Talk: Chaos in the Gravitational Three-Body Problem
Nathan Leigh (University of Concepción Chile)
The gravitational three-body problem has a long history, extending all the way back to Sir Isaac Newton. In spite of hundreds of years of research, we still do not have a complete solution to the general case, where no restrictions are placed on the nature of the interaction. Historically, this has been attributed to the appearance of chaos in large regions of parameter space, implying that a probabilistic theory is the only way to go. In this talk, I will briefly review the general three-body problem and its present-day astrophysical significance. I will then go on to introduce a probabilistic solution for the outcomes of chaotic three-body interactions mediated by gravity, and describe how my collaborators and I are using this new tool to build a model that evolves entire populations of binary stars in dense star clusters due to three-body interactions with single stars. The model is entirely analytic, and covers regions of parameter space that are only accessible to modern simulations with great computational cost.
Remote Talk: Probing dust emission in high-redshift galaxies using FIRE simulations
Lichen Liang (University of Zurich / Canadian Institute for Theoretical Astrophysics)
Fruitful information about the galaxy properties can be derived from the spectral energy distribution (SED) of the dust thermal continuum, including the star formation rate (SFR) and dust and gas mass of galaxies, which are critical for understanding galaxy evolution. In practice, however, this can be challenging at high redshifts because most high-z objects have merely a few photometric data points in the dust SED owing to the high confusion noise of the infrared instruments and limited number of bandpasses available. To infer LIR (and hence SFR) and gas mass of high-z galaxies thus requires understanding how far-infrared dust SED is shaped, which is the main topic of this talk. I will show the results obtained from the recent studies using the latest FIRE (Feedback in Realistic Environments) simulations coupled with radiative transfer technique. Specifically, I will discuss the physical mechanisms for shaping the far-infrared SED of galaxies, with a particular emphasis on the role of dust opacity and dust temperatures. In addition, I will discuss the physical origin of the IRX-βUV relation, a technique commonly adopted for deriving LIR of galaxies based the UV data alone, and assess the different sources of both the intrinsic scatter as well as the observational biases of this relation. The results to be presented link the theoretical study of galaxies at high redshift to observational constraints, which provide new insights into the growth of galaxies and the physical processes driving the cosmic star formation history.
Remote Talk: Monitoring for serendipity – the cure to boredom
Gordon MacLeod (HartRAO)
Serendipity is enhanced via time domain observations at multiple transitions in several molecules increases. The Maser Monitoring Organisation (M2O) was created by an international group of researchers, telescope managers, and students, to confirm, coordinate, and collaborate on maser monitoring and associated phenomena. Its success is evident in a plethora of publications on bursting water masers and significant accretion events. This presentation is a compilation of primarily HartRAO observations of maser monitoring, augmented by M2O observations, towards accretion events and other interesting results associated with High Mass Star-Forming Regions. Serendipity is our friend!
Remote Talk: The Constancy of GMC Surface Densities in the Milky Way and Nearby Galaxies
Charles J. Lada (Harvard-Smithsonian Center for Astrophysics)
The mass-size relation for Giant Molecular Clouds (GMCs) is one of the fundamental scaling relations of star formation. Infrared extinction studies of local (<0.5 kpc) and nearby (<3.0 kpc) clouds show that GMC masses scale with the square of GMC sizes to an exquisite degree of precision, indicating that such clouds are characterized by a constant mean surface (or column) density. In this talk I will discuss how cloud structure, as measured by the column density-probability density functions (N-pdfs) of GMCs leads to the high degree of constancy in measured GMC surface densities of local and nearby clouds. These results imply that GMCs, sites of all star formation in galactic disks, cannot obey the Kennicutt-Schmidt scaling relation. I will also report results of a recent analysis of CO derived mass-size scaling relations for GMCs across the entire Milky Way. The CO relations are consistent with infrared relations but are characterized by considerably more scatter. Close examination of the much larger scatter observed in the CO relations revealed a systematic variation in the coefficient of the mass-size relation with Galactic radius. This radial variation arises from both a radial dependence of X(CO) on metallicity and an increase in the measured surface densities of GMCs within the molecular ring. The latter increase may reflect both an intrinsic increase in cloud surface densities and a systematic upward bias in the measurements due to cloud blending in the molecular ring. I will suggest that the apparent contradiction between between a constant GMC surface density and the presence of a Kennicutt-Schmidt relation in galactic disks can be resolved by a combination of the presence of radially dependent beam dilution in the extragalactic observations and physical variations in the coefficient of the mass-size relation within and between galaxies.
Remote Talk: Studying star formation from the stratosphere with the Balloon-borne polarimeter BLASTPol
Laura Fissel (Queen’s University)
An important mystery in astrophysics is why the conversion of diffuse interstellar gas into stars is such an inefficient process. We typically observe of order 1% the star formation rate expected from a free-fall gravitational collapse of molecular gas clouds. This low efficiency is likely due to regulation from a combination of turbulent gas motions, magnetic fields, and feedback from young stars. Of these processes the role played by magnetic fields is particularly poorly understood, largely because of the difficulty of observing distant magnetic fields. In this talk I will discuss what we have learned about magnetic fields in star-forming regions using the Balloon-borne Large Aperture Sub-mm Telescope for Polarimetry (BLASTPol). BLASTPol launched from Antarctica in 2010 and 2012, operating while suspended from 10^6 cubic meter stratospheric balloon 38km above sea level (above 99.5% of the Earth’s atmosphere). By mapping polarized radiation at sub-mm wavelengths from dust grains aligned with their local magnetic field BLASTPol was able to create highly detailed magnetic field maps of the nearby giant molecular cloud Vela C. We find that in Vela C magnetic fields play an important role in the formation of both low- and high-density molecular gas sub-structures. I will also discuss our recent adventures launching a next-generation balloon-borne polarimeter, BLAST-TNG, from Antarctica in January 2020. I will finish by discussing prospects for combining dust polarization observations with Zeeman splitting measurements to build a more complete model of magnetic fields in molecular clouds.
Remote Talk: New Insights into the Milky Way Magnetic Fields through Radio Broadband Spectro-polarimetry
Yik Ki (Jackie) Ma (Australian National University & Max Planck Institute for Radio Astronomy)
Magnetic field is an essential constituent of the interstellar medium of galaxies. An accurate characterisation of the magnetic field strength and structure of the Milky Way is crucial for complete understanding of many Galactic astrophysical processes. The Faraday rotation effect can be exploited to reveal the strength and direction of the magnetic field component parallel to the line of sight, which are imprinted in the rotation measure (RM) values obtained from radio polarisation observations. In this talk, I will present the results from our efforts in gaining new insights into the magnetic fields of the Milky Way by two different ways, both from utilising the broadband spectro-polarimetric capability of the Karl G. Jansky Very Large Array (VLA) in L-band (1-2 GHz). Firstly, we investigated in the reliability of the NRAO VLA Sky Survey (NVSS) RM catalogue, which is indispensable for the modelling of the global Milky Way magnetic field. In particular, we quantified the effects of npi-ambiguity and off-axis instrumental polarisation on the RM catalogue, and unlocked the full potential of the NVSS RM catalogue for careful studies of Galactic magnetism. Secondly, we performed new radio observations for a direct study of the magnetic fields near the Milky Way mid-plane in the first Galactic quadrant. Our new observations led to a drastic increase in the number of reliable RM values by a factor of five in the target sky region. From the new data, we discovered new features in the Galactic magneto-ionic medium, with important implications on the magnetic field ordering mechanism of galaxies.
Remote Talk: MeerKAT and the South African Inter-University Institute for Data Intensive Astronomy
Russ Taylor (University of Cape Town)
In 2012 the international SKA Organization decided to site the SKA-mid frequency telescope in Africa, hosted by an eight-country African partnership. SKA-mid will be an array of thousands of parabolic antennas spread out over baselines of thousands of kilometres. As a first step toward SKA-mid, South Africa has constructed MeerKAT, a 64-element array of 13.5-m offset parabolic antennas at the African SKA central site. MeerKAT is a precursor of the SKA mid-frequency dish array, and following several years of operation as a South African telescope will be incorporated into the SKA phase 1. The MeerKAT science program consists of a small number of key-science, legacy-style, Large Survey Projects, plus open time available for new proposals. The Large Survey Projects are direct pathfinder to key science programs being planned for the SKA.
The completion of MeerKAT foreshadows one of the most significant data challenges of the coming decade and the beginning of an era of big data in African astronomy. The new South African Inter-University Institute for Data Intensive Astronomy (IDIA) has been set up to build capacity in Africa to meet the data challenge of the SKA in Africa. I will present an update on the MeerKAT and the key science programs, and discuss the related developments in data science and technologies at IDIA.
Remote Talk: Threads & flows in the dusty universe: Importance of astronomical polarimetry and spectroscopy in star forming regions
Archana Soam (SOFIA Science Center, USRA)
Role of magnetic fields (B-fields) and turbulence in star formation is still under debate but considering the magnetized nature of molecular clouds, we expect B-fields to have a significant impact on this process. Observations of molecular clouds in different environments using different astronomical techniques helps in understanding the various important aspects of star formation. I mostly worked towards mapping B-fields in nearby low mass star forming regions in different environments viz. molecular clouds in isolation and HII regions at their different evolutionary stages using multi band polarization observations. This was done using optical, near-IR, and sub-mm polarization observations to map B-fields from parsec to sub-parsec scales (mostly at the distances of Taurus and Orion). In this talk, I will briefly present the maps of B-fields in various regions i.e. cores, filaments, BRCs (bright-rimmed clouds). Besides B-fields, I shall briefly discuss our attempts to understand the kinematics of BRCs and Radiation Driven Implosion (RDI) process in HII regions investigated using various molecular line observations. In addition, I will briefly introduce some of my ongoing work on understanding dust grain alignment and polarization efficiency in molecular clouds.
Remote Talk: A Census of High-Mass Star Formation Throughout the Milky Way
Will Armentrout (Green Bank Observatory)
HII regions are the archetypical tracers of high-mass star formation. Because of their high luminosities, they can be seen across the entire Galactic disk from mid-infrared to radio wavelengths. A uniformly sensitive survey of Galactic HII regions across the disk would allow us to constrain the properties of Galactic structure and star formation. We have cataloged over 8000 HII regions and candidates in the WISE Catalog of Galactic HII Regions (astro.phys.wvu.edu/wise), but only ~2500 of these are confirmed HII regions. From our WISE survey completeness limits, we set a lower limit of 7,000 Milky Way HII regions created by a central star of type B2 or earlier. Population synthesis modeling suggests there are closer to 10,000 Galactic HII regions. We have not yet confirmed the vast majority of the Milky Way’s HII regions.
A population of especially interesting HII regions trace the Outer Scutum-Centaurus spiral arm (OSC), the most distant molecular spiral arm in the Milky Way. These regions represent star formation at low densities and low metallicities, similar to the conditions in galaxies like the Large Magellanic Cloud or a much younger Milky Way. To date, we have detected high-mass star formation at 17 locations in the OSC, with the most distant source at 23.5 kpc from the Sun and 17 kpc from the Galactic Center. They have molecular cloud masses up to 10^5 Msol and central stellar types as early as O4. By comparing molecular and stellar masses, we can begin to put constraints on the star formation efficiency of these distant outer Galaxy sources. We map the ionized gas using the Very Large Array at X-band in the D-configuration. We map the 13CO, HCN, and HCO+ molecular gas emission using the Argus array on the Green Bank Telescope, producing individual 5 arcmin maps with 8 arcsec resolution and 0.5 K sensitivity in 20 minutes.
Remote Talk: Rethinking Interstellar Dust: Insights from Microwave Emission and Polarization
Brandon S. Hensley (Princeton University)
The highly polarized emission from Galactic dust as seen by the Planck satellite has challenged our basic assumptions about the makeup of interstellar grains. In the first part of this talk, I will introduce a new model of interstellar dust that posits that the silicate and carbonaceous materials largely reside on the same grains, an idealized mixture we term “astrodust.” I will demonstrate the compatibility of the astrodust-based model with existing observations and highlight how it can be tested with future data. In the second part of this talk, I will present new results on the nature of the anomalous microwave emission (AME), its polarization properties, and its connection to spinning nano-grains, including PAHs. I will conclude with a mysterious extragalactic AME source that appears incompatible with either spinning dust emission or emission from a background radio galaxy, and welcome any discussion and insights.
Remote Talk: Young Stellar Objects in the Multiwavelength Time Domain
Lynne Hillenbrand (Caltech)
During their first few million years, protostars and pre-main sequence stars exhibit a wide range of inflow (accretion) and outflow (jet/wind) activity. Myriad processes occurring both on the stellar surface, and in the inner circumstellar regions, contribute to time-variable phenomena that are observed over much of the electromagnetic spectrum. Individual young stars can be predictably or enigmatically variable. The talk will begin with an overview of the relevant phenomena, then proceed to discuss recent work on state-of-the-art time domain data sets that are providing new insights.
Remote Talk: Galaxies and Their Satellite Populations
Gwendolyn Eadie (U of T David A. Dunlap Department of Astronomy and Astrophysics)
In this talk, I will touch on two projects about galaxy satellite populations that make use of concepts and methods from applied statistics. The first project focuses on estimating the mass of the Milky Way Galaxy using the kinematics of its dwarf satellite populations. I will discuss how our mass estimates — which use equilibrium assumptions — lend possible evidence to the idea that the LMC may be significantly affecting the kinematics of tracers around the Milky Way at certain distances. The second project focuses on the relationship between a galaxy’s total stellar mass and its mass in globular clusters. I will discuss how we have identified and quantified a transition mass region over which galaxies of a given stellar mass can be assigned a probability of having a GC population. Both of these projects use methods from applied statistics such as hierarchical Bayesian analysis, logistic regression, and a Bayesian hurdle model. Thus, during the talk I will introduce and describe each of these methods and highlight their advantages in these projects.
Remote Talk: Nature’s Death Stars: A Discussion of Supermassive Black Holes, Relativistic Jets, and The Event Horizon Telescope
Nicholas MacDonald (Max Planck)
What are relativistic jets made of? The answer is central to our understanding of how supermassive black holes influence their surrounding galactic environments. In this talk I will present my research on the composition of relativistic jets (and in particular blazars) within the context of the Event Horizon Telescope (EHT) collaboration.
Blazars represent an extreme subclass of active galactic nuclei (AGN), in which an accreting supermassive black hole launches and powers a relativistic jet of magnetized plasma that is closely aligned to our line-of-sight. Blazar jets: (i) shine across the entire electromagnetic spectrum (from low-frequency radio waves to high-energy gamma-rays), (ii) exhibit dramatic flares, and (iii) dominate the high-energy extragalactic sky. Very long baseline interferometric (VLBI) arrays (such as phased ALMA & The Event Horizon Telescope) are capable of imaging the polarized synchrotron emission emanating from the innermost regions of relativistic blazar jets with unprecedented angular resolution and sensitivity. In particular, the linearly and circularly polarized synchrotron emission from blazars carry imprints of both the strength and orientation of the collimating magnetic fields as well as the plasma content of each jet. In parallel to these advances in VLBI imaging, modern computational resources now support the production and execution of increasingly sophisticated 3D numerical jet simulations, from semi-analytic shock-in-jet and turbulence models, to relativistic magneto-hydrodynamic (RMHD) and particle-in-cell (PIC) jet plasma simulations.
My research focuses on bridging the gap between these 3D relativistic jet simulations and mm-wave global VLBI observations of blazar jets through the application of ray-tracing and polarized radiative transfer. In this talk, I will present a suite of relativistic jet simulations that attempt to place firmer constraints on the as yet unknown plasma content of black hole jets.
Remote Talk: Early Results from VERTICO: the Virgo Environment Traced in CO Survey
Toby Brown (HAA)
The Virgo Environment Traced in CO survey (VERTICO) is a pioneering Atacama Large Millimeter/submillimeter Array (ALMA) large program that is investigating the effect of environment on molecular gas by mapping the distribution and kinematics of molecular across 51 Virgo Cluster galaxies on sub-kpc scales. As the critical final component of a diverse, homogeneous legacy dataset, VERTICO is revealing how physical mechanisms such as ram pressure stripping drive the star formation process in dense environments in unmatched detail. This talk will showcase the early results from the VERTICO team, highlighting evidence for the ability of environment to reach far into galaxies, perturbing molecular gas discs and dictating the efficiency of the star formation process.
Remote Talk: Cluster formation and gas kinematics in high mass clouds
Amelia Stutz (University of Concepción Chile)
By observationally scrutinizing the nearest high mass clouds and protoclusters, we gain new insights into cluster formation physics. The Integral Shaped Filament (ISF) is home to the nearest significant protocluster, the Orion Nebula Cluster (ONC/M42). Based on a high density of observables of both the gas and stars, we previously proposed the “slingshot” mechanism, requiring that the gas ISF oscillate ejecting stars. The B-field morphology (possibly helical) and strength, compared with the gas mass distribution, indicates that magnetic instabilities may be propagating through the cloud driving the oscillations in the ISF. These may be responsible for the slingshot. The gas kinematics exhibit twisting and turning features that may be consistent with rotation and helical structures in the dense gas. We show that the stellar density follows a Plummer profile while the gas follows a cylindrical power law. The stellar contribution to the gravitational field is nearly equal to that of the gas at r=a. At all other radii the field is gas-dominated. The cluster crossing time is ~ 0.5 Myr, nearly identical to the filament oscillation timescale. These results reveal an intimate connection between the stars and the gas, such that tidal effects due to filament oscillations may set the protocluster structure. That is, the gas density regulates the star density in the ONC. Meanwhile, in California cloud, which has the same mass as Orion but is at an earlier evolutionary stage (~1/10th the protostars), we detect rotation in cluster-forming filament L1482. Results in extragalactic systems show that cloud rotation is set by the overall galaxy rotation and not consistent with e.g. cloud-collision models. Combined, these results may indicate that velocity gradients in Milky Way protoclusters are naturally explained by rotation, which is established on large scales of galaxy disks and then percolates down to protocluster and possibly even to the tiny scales of protostars.
Remote Talk: Supernova Remnants As A Probe Of Galactic Magnetism Revealed By THOR
Russell Shanahan (University of Calgary)
Broadband radio polarimetry of supernova remnants (SNRs) allows us to investigate the magnetic field structure in the SNRs, as well as the Galactic environment along the line-of-sight. The HI/OH Recombination line (THOR) survey provides broadband radio continuum observations with polarization of a large section of the inner Galaxy. With high angular resolution, we discover small-scale polarization features that reveal a rich structure in the magnetic field of the SNRs. Our investigation also reveals evidence of Faraday rotation internal to the SNRs, in addition to Faraday rotation in the interstellar medium along the line-of-sight. Since SNRs have different distances, the Faraday rotation we observe can be used to probe the Galactic magnetic field as well as kinematic tracers of Galactic structure.
Remote Talk: UV Spectro-Polarimetry in the Solar Atmosphere: New Approach to Address the Solar Mystery Using Two Sounding Rocket Experiments
Takenori Joten Okamoto (NAOJ and ISAS/JAXA)
Magnetic fields in the solar atmosphere play an important role in the energy transfer from the solar surface to the hotter atmosphere “corona”, which provide fundamental information to solve the remaining puzzle of “the coronal heating problem”. Measurements of the magnetic field in the chromosphere, which is sandwiched by the solar surface and the corona, is essential to achieve the goal. In 2015 and 2019, we performed two sounding rocket experiments, CLASP1 and CLASP2, to establish the techniques to diagnose the chromospheric magnetic field by demonstrating the maturity of the ultraviolet spectro-polarimetry for future development into a satellite.
From these experiments, we successfully detected significant polarization signals with high accuracy (<0.1%) in the UV spectra for the first time. Our findings are as follows: (1) We confirmed the theoretically-predicted scattering polarization both in the hydrogen Ly-alpha (121 nm) and Mg II h & k (280 nm) lines. The spatially-varying linear polarization should contain magnetic field information via the Hanle and Magneto-Optical effects. (2) We detected clear circular polarization signals in the Mg II and the Mn I lines around 280 nm, which are induced by the Zeeman effect. We derived the spatio-temporal variations of the line-of-sight field strength at three different heights of the upper/middle/lower chromosphere. (3) We measured the center-to-limb variation in Stokes Q/I of Ly-alpha with imaging polarimetry by the slit-jaw instrument.
The successful observation of polarization indicative of magnetic fields in the solar atmosphere, in particular in the upper chromosphere, means that UV spectro-polarimetry has opened a new window to such solar magnetic fields, allowing us to see new aspects of the Sun.
In this seminar, I will show the results of these missions as well as an introduction of solar observations and the scientific interests.
Remote Talk: Polarization analysis of evolved intermediate mass stars.
Laurence Sabin (Universidad Nacional Autónoma de México)
Post-AGB stars and Planetary Nebulae represent the advanced evolutionary phase of the low and intermediate -mass stars. Although this stage is short-lived, several physical and chemical processes (important for stellar evolution) are occuring and can be traced and analysed using multi-wavelength polarimetry techniques. For instance the properties of the circumstellar dust expelled into the ISM, the magnetic fields believed to be responsible (in part) for the departure from spherical symmetry are some of the topics that are investigated via polarimetry. I will therefore discuss the results obtained in this field of study, this includes the scientific investigations, the instrumental developments but also the constraints.
Remote Talk: Global MHD galaxy simulations: the effects of feedback and the emergence of a mean-field dynamo
Evangelia Ntormousi (Scuola Normale Superiore di Pisa, Italy)
Magnetic fields are of paramount importance for understanding the evolution and dynamics of galaxies. However, even the magnetic field of our galaxy is still largely a mystery, since its strength and direction are impossible to measure simultaneously. It is therefore essential that we complete our knowledge with numerical simulations of galaxy and magnetic field co-evolution.
In this talk I will present results from a series of high-resolution numerical models, aimed at deciphering the effect of the initial conditions and of stellar feedback on the evolution of the galactic magnetic field in isolated, Milky Way-like galaxies. The models include a dark matter halo, a stellar and a gaseous disk, star formation and supernova feedback, so that the dynamical evolution of the galaxy is self-consistent.
We find that, independently of the initial conditions, the galaxies quickly develop a turbulent velocity field and a random magnetic field component very early in their evolution.
We also show for the first time that a mean-field dynamo naturally occurs as a result of the dynamical evolution of the galaxy, and amplifies the magnetic field by an order of magnitude over half a Gyr.
By following the growth of the magnetic field in a complex galactic environment, these models bring us a step closer to understanding the cosmic origin of magnetic fields.
Remote Talk: FYST/CCAT-prime: a submillimetre-wave survey facility
Michel Fich (Waterloo Centre for Astrophysics)
The Fred Young Submillimeter Telescope (FYST) is under construction by the international CCAT-prime project team. FYST will be located at a superb site in northern Chile and with an innovative design and excellent surface it will be capable of extremely wide-field observing at the shortest submm wavelengths accessible from the surface of the Earth. Researchers in the US, Germany, and Canada are developing instruments that will utilize the wide-field capability and enable large-scale surveys that will address a wide range of areas in cosmology, galaxy evolution, and galactic structure. In this talk I will briefly describe the site, the telescope, the instruments, the science plans and highlight the Canadian contributions to the project.
Remote Talk: Bifurcation of planetary building blocks during Solar System formation
Tim Lichtenberg (University of Oxford)
The origin of the Solar System shapes our understanding of the physical and chemical processes that drive planetary formation and early evolution. Geochemical analyses of meteoritic materials and astronomical observations of circumstellar disks provide evidence for a fragmented planet formation process. In the Solar System this manifested as two spatially and temporally separated reservoirs that accreted to form the inner, volatile-depleted and outer, volatile-rich planetary populations. The origin of this dichotomy is unknown. In this talk I will discuss our recent work on how the build-up and earliest evolution of the solar protoplanetary disk can influence the timing of protoplanet formation and their internal evolution. Migration of the water snow line during the Class I and Class II disk stage can generate two distinct bursts of planetesimal formation that sample different source regions of interstellar materials. These reservoirs evolve in divergent geophysical modes and develop distinct volatile contents, consistent with constraints from planetary accretion chronology and volatile composition, thermochemistry of extraterrestrial materials, and the mass divergence of inner and outer Solar System. Our simulations suggest that the compositional fractionation and isotopic dichotomy of the Solar System observed today was initiated by the interplay between disk dynamics, heterogeneous accretion, and internal evolution of forming protoplanets.
Remote Talk: Indigenous astronomy and Navigation
Ray Norris (CSIRO)
Aboriginal people in Australia have a rich astronomical tradition such as the “Emu in the Sky” constellation of dark clouds, and stories about the Sun, Moon, and stars, revealing a depth and complexity of pre-contact Aboriginal cultures which are not widely appreciated by outsiders. Not only did they know the sky intimately, but they were familiar with planetary motions, tides, and eclipses. Their songs and stories show that Aboriginal Australians sought to understand their Universe in a similar way to modern science. They used this knowledge of the sky to construct calendars, songlines, and other navigational tools, enabling them to navigate across the country, trading artefacts and sacred stories
Remote Talk: Biogenic Worlds: From atmospheric HCN production to the building blocks of RNA in warm little ponds
Ben K. D. Pearce (McMaster University)
What is the origin of the building blocks of life on early Earth? Is it necessary that they were delivered by meteorites or interplanetary dust? Or was early Earth “biogenic,” and could produce key biomolecules on its own? An atmosphere rich in HCN is a distinguishing feature of what we term biogenic worlds. HCN is a key species produced in Miller-Urey electric discharge experiments simulating lightning-based chemistry in the primordial atmosphere. HCN reacts in water to form nucleobases and ribose, the building blocks of RNA, and amino acids, the building blocks of proteins. To determine whether early Earth was biogenic, we develop a self-consistent chemical kinetic model for the production and rainout of HCN in the early atmosphere, and couple it to a comprehensive model of warm little ponds to compute the in situ production of the building blocks of RNA. We model two epochs of the Hadean eon, at 4.4 bya (billion years ago) and 4.0 bya, which differ in composition, luminosity, UV intensity, and impact bombardment rate. At 4.4 bya, UV intensity was high due to the active newly formed Sun, and asteroids and comets were bombarding the planet at an overwhelming rate of 1×1013 kg/yr. Impact degassing at this time produced a reducing, H2-dominant atmosphere. At 4.0 bya, the atmosphere was depleted in hydrogen due to escape from the upper atmosphere, and volcanic outgassing led to an oxidizing CO2-dominant world. The reducing models at 4.4 bya lead to RNA building block production in ponds that is comparable in concentration to what would result from meteoritic delivery (ppm-range). Unlike the RNA building blocks delivered to ponds by meteorites, which survive for less than a few years, the concentrations produced in situ are maintained indefinitely due to the steady influx of HCN from the troposphere. The oxidizing models at 4.0 bya lead to substantially lower RNA building block concentrations (ppq-range). These results suggest that early Earth was biogenic at 4.4 bya and remained so for at least 100 million years, but was over by 4.0 bya due to oxidation of the atmosphere.
Remote Talk: Solar Observations with CHIME
Dallas Wulf (McGill University, CHIME)
In 2019, the CHIME collaboration began a Solar observing campaign with the objective of measuring the telescope’s primary beam response. The Sun is often overlooked as a calibration source at radio frequencies, owing to its spatial and spectral variability on timescales ranging from seconds to years. However, by taking advantage of observations made near Solar minimum, the magnitude of these effects can be reduced to∼10% at decimeter wavelengths. The extreme radio brightness of the Sun, combined with its semiannual span of declination, enable measurements which probe over 1,600 square degrees of beam solid angle with ~30 dB of dynamic range. I’ll present the results of this work and describe the utility of this unique data set in the context of calibrating driftscan instruments.
Remote Talk: A Comparison of Magnetic Field Tracers in the Warm Ionized and Cold Neutral Filamentary Interstellar Medium
Jessica Campbell (University of Toronto)
Magnetic fields are fundamental to understanding our Milky Way Galaxy. Yet, measuring the three-dimensional multi-phase Galactic magnetic field (GMF) remains a considerable challenge, largely because each probe is sensitive to one- or two-dimensional projections of the field in different phases of the ISM. For instance, the spatial gradient of polarized radio emission is sensitive to the line-of-sight field strength in the relatively rarefied warm ionized gas, while narrow structures in HI emission highlight the plane-of-sky field orientation in the dense cold neutral gas. As a result, very little is understood about how the GMF threads the multi-phase ISM. I will discuss our search for a common magnetic field shared between the warm ionized and cold neutral ISM by comparing 1.4 GHz GALFACTS polarization gradients to linear diffuse/translucent GALFA-HI structures. I will then highlight a unique high-Galactic latitude region that we found to contain an alignment between polarization gradient filaments and narrow HI structures, and will conclude by discussing the lack of observed global alignments found between these multi-phase tracers of the magnetized ISM.
Remote Talk: SOFIA: Revealing Interstellar Magnetic Fields from the Stratosphere
Simon Coudé (USRA)
The Stratospheric Observatory for Infrared Astronomy (SOFIA) is the largest airborne observatory in the world, and its ability to fly above most of the water vapor in the atmosphere makes it uniquely suited to study the Universe at mid- and far-infrared wavelengths. The multi-wavelength polarimetric capabilities of the High-resolution Airborne Wideband Camera Plus (HAWC+) in particular provide a window into the dynamics of the interstellar medium in our galaxy and others. Indeed, the polarization signature from dust thermal emission is an effective tracer of magnetic fields in a wide variety of environments. Measuring these fields is necessary to quantify several phenomena, such as the energy balance at different stages of the star formation process. Polarization measurements at multiple wavelengths can also improve our understanding of dust physics by probing their alignment efficiency to magnetic fields and the interstellar radiation field. This talk will present recent polarization results obtained with HAWC+, and how they synergize with longer-wavelength data from other observatories. We will also cover some of the unusual challenges of doing astronomy from the stratosphere aboard an experimental aircraft.
Remote Talk: Fast radio burst detection and morphology with the CHIME telescope
Ziggy Pleunis (McGill University, CHIME)
Fast radio bursts (FRBs) exhibit a variety of time-frequency structures, shaped by an unknown emission mechanism and transformed by propagation through an ionized and inhomogeneous medium. FRBs comprised of downward-drifting sub-bursts seem ubiquitous among repeating sources of FRBs but have so far not been seen in one-off FRBs. The Canadian Hydrogen Intensity Mapping Experiment (CHIME) is a 4-cylinder 80-m x 100-m transit radio interferometer, located at the Dominion Radio Astrophysical Observatory near Penticton, B.C. The CHIME/FRB experiment has recently released a first catalog of >500 FRBs, 62 of which are bursts from 18 different repeater sources, detected in the 400-800 MHz octave, all detected with the same instrument and a similar selection function. With this first catalog, we confirm that repeater bursts, on average, have larger widths and we show, for the first time, that repeater bursts, on average, are narrower in bandwidth. This difference could be due to a beaming or propagation effect, or it can be intrinsic to the populations. I will also present the lowest-frequency FRBs, detected with the LOw Frequency ARray (LOFAR) telescope by following up CHIME/FRB-discovered repeating sources.
Remote Talk: Finding Our Place in the Night Sky
Jennifer Howse (University of Calgary, Rothney Astrophysical Observatory)
The Convergence: Where the people of the land greet the sky project is the collaborative development of a scientific and Indigenous themed astronomy. Our primary theme is creating connections to the land and sky though traditional Indigenous Ways of Knowing and current RAO research initiatives. Time and space are cultural as well as astronomical and this exhibit welcomes diverse voices and represents our community’s relationship to the universe. Astronomy is the world’s oldest science and it is fundamental to the traditional conscious of the Indigenous peoples of Canada. Creating relevant Indigenous content for all of our spaces, programs, and engaging Indigenous students, is a priority for the Rothney Astrophysical Observatory and is part of the University of Calgary’s strategy ii’ taa’poh’to’p.
Remote Talk: The physics of dense gas formation in the Musca cloud
Lars Bonne (SOFIA Science Center, USRA)
I will present a case study of the Musca cloud to evaluate the role of gravity, turbulence and the magnetic field in the formation of dense filamentary gas that will end up forming stars.
In the first part, I will present molecular line observations that unveil organized kinematics in the Musca cloud, yet the dense filament is at a remarkably redshifted velocity in the cloud. This indicates that the magnetic field is bent around the dense Musca filament which drives continuous mass inflow to the filament. Combining these results with a study of HI data towards the full Chamaeleon-Musca complex points to a scenario where this bending of the magnetic field, and the resulting dense gas formation, was initiated by a large scale (~ 50 pc) HI colliding flow.
In the second part, I will present a pilot study, focusing on the Musca cloud, to extract the turbulent properties of a molecular cloud from Herschel maps using microcanonical multifractal analysis. This reveals a turbulent cascade at scales below 1 pc and that turbulence dissipation occurs non-uniformly in localized regions of strong dissipation over the Musca cloud. This could fit with indications of warm gas, obtained from the analysis of higher-J CO lines, around the Musca filament.
Finally, I will try to propose a coherent scenario to explain these observations towards Musca and discuss how some of these results compare to observations towards other clouds.
Remote Talk: Atomic Gas in Nearby Galaxies as a Cosmological Probe
Kristine Spekkens (RMC/Queens University)
The atomic gas (HI) content of nearby galaxies provides important insight into how they form and evolve within the standard cosmology. In this talk, I will highlight some of my group’s recent efforts to build statistical samples of HI detections for nearby galaxies to use as cosmological probes. I will first focus on how sensitive single-dish observations of dwarf satellite and ultra-diffuse galaxies are a powerful tool for measuring their structure and constraining formation models. I will then describe how the WALLABY widefield HI survey that will soon begin on the Australian SKA Pathfinder (ASKAP) will allow for the first spatially resolved HI population studies, and present early results from the pilot survey phase.
Remote Talk: Optical Polarimetry and the Galactic Magnetic Field
Antonio Mario Magalhaes (University of São Paulo)
Interstellar optical polarization is produced by dust grains aligned by a magnetic field and can be used as a tracer of the latter. We discuss some results of our Interstellar Polarization Survey and what we have learned about the magnetic field structure of the Galaxy at small and large scales. The data include the Local Interstellar Medium (ISM) and the nature of the SMC dust and its magnetic field structure. We also look into intriguing data concerning the relationship between the ambient magnetic field direction and the orientation of disks around young stars in the Galaxy.
We describe the numerical tools we are currently developing towards a Galactic Magnetic field model. It combines radio (synchrotron) and optical data and a dust model which aims at explaining the observations. Applications of this model include the interpretation of our optical polarization data towards cosmological fields.
Finally, we describe our plans for SOUTH POL, a forthcoming survey of the whole Southern sky in optical polarized light. SOUTH POL will impact several areas, from Cosmology to Solar System studies.
Remote Talk: Near and far: How radio maps reveal the structure of our Milky Way’s magnetic field
Jennifer West (Dunlap, University of Toronto)
Our view of the sky is a complicated superposition of objects that are both near and far. Disentagling this information is challenging, but essential to a complete understanding of our Galaxy, and the Universe. In this talk, I will discuss the brightest, large-scale, diffuse, polarized radio features in the sky, the North Polar Spur and the Fan Region, and present a model that explains these features as very local structures in our Galaxy’s magnetic field. I will also discuss some of the challenges with and present some of the ways that we can understand the global structure beyond our Local Bubble.