Latest results from CHIME/FRB
Paul Scholz (UofT)
CHIME/FRB is a search for fast radio bursts using the CHIME telescope at DRAO. As we enter into its second year of operation, several exciting results which help to elucidate the nature of FRBs have come out of CHIME/FRB. I will review the current status of the project and present the latest results, putting them in context in the FRB field.
Unlocking the Radio Sky – mapping transients and cosmic structure with CHIME and the path to CHORD
Matt Dobbs (McGill)
Technology advances have opened a new era of radio observations. We are now monitoring the sky at millisecond cadence and discovering a vast catalog of new fast radio transients while simultaneously making deep maps of structure in the universe using hydrogen intensity mapping as a tracer. While these fields are still in their infancy, early results are rolling out, fuelling discovery and motivating the design for new instruments. I will show recent advances with the CHIME telescope, and describe the path towards developing CHORD, a new generation highly redundant telescope to be sited at DRAO.
Supernova Archaeology: Uncovering the progenitors of Type Ia supernovae from clues in the ISM
Tyrone Woods (DAO)
Type Ia supernovae (SNe Ia) have proven vital to our understanding of cosmology, both as standard candles and for their role in the origin of the elements. They are now understood to arise from the thermonuclear explosion of a white dwarf, but why should a white dwarf explode? Evolutionary models can be grouped into either “accretion” or “merger” scenarios, with accretion models typically implying a hot, luminous phase prior to explosion. These objects are significant sources of ionizing radiation; therefore, the environment surrounding SN Ia progenitors should be strongly ionized, and traced by faint nebular emission. Such “relic” nebulae should extend out to 10 — 100 parsecs and linger for roughly the recombination timescale in the ISM (∼100,000 years). In this talk, I’ll show how the absence of a surrounding nebula excludes any accretion (“single-degenerate”) channel for the origin of Tycho’s supernova, as well as many other nearby remnants. Most variations on the merger (“double degenerate”) scenario remain viable. I’ll also show how a similar test can be applied to the integrated emission of old stellar populations, ruling out the textbook accretion scenario for delay times greater than 1 Gyr, before concluding with some recent results on the deeper connections between binary progenitors of some supernovae and the warm ionized interstellar medium.
Weak Lensing of 21cm Maps
Simon Foreman (Perimeter)
Gravitational lensing of the cosmic microwave background (CMB) has emerged as a powerful probe of cosmology, made possible by the development and characterization of nearly-optimal estimators for extracting lensing-induced distortions from temperature and polarization maps. One can ask whether similar tools can be applied to upcoming “intensity maps” of emission lines at various wavelengths (e.g. 21cm). Following an introduction to the essential concepts of CMB lensing, I will present recent work in this direction, focusing on the impact of nonlinear gravitational clustering on standard CMB lensing estimators when applied to intensity maps. I will show how these nonlinearities can provide a significant contaminant to lensing reconstruction, but will also describe how this contamination can largely be mitigated by modifying the lensing estimator. Finally, I will present estimates for the detectability of lensing in ongoing and proposed intensity mapping surveys, and highlight related work on reconstructing large-angle information in optical galaxy surveys using the same techniques.
The Dynamic Radio Sky from the Owens Valley Radio Observatory
Gregg Hallinan (Caltech)
I will discuss a new generation of radio arrays designed to rapidly survey the radio sky from the Owens Valley Radio Observatory (OVRO) in California. The 352-dipole Long Wavelength Array (OVRO-LWA) images the entire sky every 10 seconds to simultaneously monitor 4000 nearby stellar systems in the search for transient radio emission from exoplanets. It will also search for prompt counterparts to LIGO events and detect 1000s of air showers from high energy cosmic-rays. Simultaneously, at GHz frequencies, the 110-dish Deep Synoptic Array (DSA) will detect and localize >100 fast radio bursts (FRBs) to their host galaxies each year. I will also introduce the DSA-2000 concept, a planned future radio survey camera for the next decade.
Mapping the Galactic Magnetic Field with Hydroxyl Masers
Chikaedu Ogbodo (Macquarie)
A comprehensive understanding of cosmic evolution requires adequate understanding of magnetic fields, which are known to pervade the universe in varying scales. Observed at the Galactic scale, magnetism plays essential roles at the onset of star formation, going from a weak diffuse interstellar field to an amplified compressed field. Diffuse and weak large-scale Galactic magnetic fields have been extensively probed using several techniques. But these field strengths are weaker by order(s) of magnitude than those found in high density regions, mostly in the Galactic spiral arms, which are hosts to high-mass star forming (HMSF). The MAGMO (Mapping Galactic magnetic field with OH masers) project is designed to investigate the correlation between field orientations observed in the diffuse large-scale medium and in high-density regions. Expected outcomes inferred by the Zeeman effect (the splitting of emission lines due to the presence of magnetic fields) on OH maser emission lines will determine if the information about the Galactic field orientation is retained after the contraction from weak large-scale magnetic fields to high densities found in HMSF regions. HMSF regions are exclusively traced by 6.7 GHz methanol masers, and we have searched for the Zeeman splitting effect in ground-state Hydroxyl (OH) masers (1612/1720/1665 and 1667-MHz OH transitions) towards 702 targets from the Methanol Multibeam Survey. In my talk I will present the complete polarimetric and detection results for the rarer 1612- and 1720-MHz OH maser transitions, partial preliminary results for the 1665- and 1667-MHz OH maser transitions, and assess the degree to which information about the Galactic-scale magnetic field orientation is revealed by their in-situ magnetic field measurements. I will also present results of the association statistics between the ground-state OH transitions, their relationship with other maser species, and the environment of their host HMSF regions.
The Parkes Ultra Wide-bandwidth Low Receiver
Jane Kaczmarek (DRAO)
Continuing the trend in astronomy to observe over larger and larger bandwidths, the team at CSIRO Astronomy & Space Science has recently designed, manufactured and installed the new Ultra-Wideband Low-frequency (UWL) receiver, which allows for the iconic 64m Parkes radio telescope to simultaneously observe from 0.7 – 4.2 GHz (6:1). With its outstanding sensitivity and polarimetric performance, as well as its ability to carry out high-time resolution astronomy, the UWL has already enhanced the outcomes of a wide range of scientific projects. Key science projects include sensitive tests of general relativity and the search for gravitational waves, the study of the interiors of neutron stars and mapping the structure of the Galactic magnetic field. In this talk, I will introduce the receiver, present recent science results and discuss the planned renewal of the entire receiver fleet on Parkes.
Antenna Array Design, Beam Calibration of the CHIME telescope and Mapping of the North Celestial Cap
Meiling Deng (DRAO)
The Canadian Hydrogen Intensity Mapping Experiment (CHIME) is a 21cm intensity mapping experiment designed to probe the nature of Dark Energy, which drives the late-time cosmic acceleration of the universe and is one of the biggest puzzles in modern physics. In this talk I will present the work I have done as a CHIME PhD student. My work mainly consists of three parts: the design of the dual-polarized cloverleaf antenna array which matches the next-stage LNA so that its effective noise is about 25 Kelvin across both the frequency domain (400 MHz to 800 MHz) and the scanning angle domain for both polarizations; the simulation and calibration of the CHIME beam for removal of the galactic foreground contamination which is 100,000 times brighter than the 21cm signal; the mapping of the north celestial cap, as a pathfinder to mapping the whole northern hemisphere for better understanding and removal of the CHIME foreground and for galactic science.
Neutral and Molecular Gas at Low Metallicity in the Small Magellanic Cloud with the ATCA, ALMA, and ASKAP
Katie Jameson (CSIRO)
The Small Magellanic Cloud (SMC) provides the only laboratory to study the detailed physics of star formation and the interstellar medium relevant to the high redshift universe. Not only is the transition from warm to cold neutral gas a rate limiting step to the formation of molecular gas, but it appears to influence star formation efficiency globally and we still do not understand how metallicity affects this transition. We present first results from a new HI and OH absorption line study using the ATCA to measure the warm-to-cold atomic fraction and the atomic-to-molecular transition in the SMC. We find very cold (~20 K) temperatures for individual cold gas clouds and an average cold HI cloud temperature of 30 K, lower than in the Milky Way, and a cold atomic gas fraction of 25% for the SMC, which is similar to the Milky Way and the Local Group. ALMA ACA CO observations of a subset of sources have only revealed detectable CO emission near one source with cold HI indicating that many regions with cold atomic gas have little CO emission and possibly no molecular gas. I will also present preliminary results from a new large (1 deg x 0.5 deg) ALMA ACA CO map of the Southwest Bar of the SMC, which shows previously undetectable small (~ 2 pc) molecular gas clumps are found throughout the region. I will compare the CO map with the new GASKAP HI observations and give an overall update on the GASKAP survey.
The CHANG-ES Project and new Results on Polarized Disks and Halos of Galaxies
Judith Irwin (Queen’s University)
CHANG-ES (Continuum Halos in Nearby Galaxies — an EVLA Survey) has surveyed 35 edge-on galaxies using the VLA in three array configurations and two frequencies. With over 400 hours of observing time and detection of all polarization products, this survey has revealed details about the disk-halo interaction and magnetic field structures that have never before been seen in any galaxy. One hundred hours of Greenbank Telescope time have also been obtained for the zero-spacing information. A mature program, more than 20 papers have now been published with the CHANG-ES moniker. This talk will highlight the results to date, including some that are surprising and unexpected.
Remote Talk: The JCMT BISTRO Survey: Variation of magnetic field and grain alignment properties within the Ophiuchus Molecular Cloud
Kate Pattle (National University of Ireland Galway)
The role and relative importance of magnetic fields in the late stages of mass assembly within molecular clouds remains highly uncertain. In this talk I will discuss recent results from the JCMT (James Clerk Maxwell Telescope) POL-2 polarimeter and the JCMT BISTRO (B-Fields in Star-Forming Region Observations) survey, which is currently mapping star-forming regions within 2 kpc of the Solar System in submillimetre polarized light. The resolution and sensitivity of the BISTRO observations allows magnetic fields to be traced from low to high densities in star-forming gas, and provides new insights into the depths into molecular clouds to which dust grains are aligned with the magnetic field. I will particularly discuss recent observations of the nearby Ophiuchus molecular cloud, a well-resolved site of low to intermediate-mass star formation. The proximity of this molecular cloud allows for detailed investigation of the variation of magnetic field morphology and dust grain alignment with local environment within an individual star-forming region. Our results demonstrate that the magnetized behaviour of individual star-forming clumps is strongly influenced by local effects and stellar feedback.
Remote Talk: Galactic Faraday tomography at low frequencies
Cameron Van Eck (Dunlap)
The new generation of low-frequency (sub-GHz) radio telescopes, particularly LOFAR and MWA, have opened up the polarized sky in new and amazing ways. We now have the capability to explore low frequency polarization at high resolution, on large angular scales, and with large fields of view, all at the same time. In my talk I will review low-frequency Faraday tomography to date, and discuss how we can take advantage of the properties of polarization at low-frequencies to inform our analysis of the observations. In some cases, we can break the degeneracies that prevent us from modelling the magnetic field along the line of sight. There are several ongoing, planned, and possible surveys that will let us break open the low frequency polarized sky.
Remote Talk: Collisions Probabilities in the Edgeworth-Kuiper belt
Abedin Abedin (DAO)
The Edgeworth-Kuiper belt is a torus shaped agglomeration of icy bodies, beyond the orbit of Neptune, encompassing the Solar System. These bodies are leftover of the formation of Solar System, and have undergone little to no chemical alteration, compared to asteroids, and therefore are considered to be relatively pristine. Today, there are more than 3000 Kuiper belt objects (KBO) discovered of size D> 30 km, which is approximately the ground and space detection limit for these distant objects. Of the sample of 3000 KBOs, more than 800 objects have well established and reliable orbits, as a result of the “Outer Solar System Origin Survey” (OSSOS) and “Canada-France Ecliptic Plane Survey” (CFEPS) surveys. These high-precision orbits allow for dynamical classification of the OSSOS and CFEPS discoveries. Using the dynamical classification of KBOs, we calculate the intrinsic collision probabilities between each different dynamical class and also the collision speed. These intrinsic collision probabilities lay the foundations for calculation of the collision rates between KBOs, given an underlying Size Frequency Distribution model of different KBO dynamical populations.
Remote Talk: Deconvolution and Calibration of CHIME Sky Maps for Galactic Science and Modelling Instrumental Effects
Joshua MacEachern (UBC)
The Canadian Hydrogen Intensity Mapping Experiment (CHIME) observes the entire northern sky between 400-800MHz to a noise-limit of ~300mJy every day. These daily full sky surveys provide an unprecedented opportunity to study our galaxy. Galactic emission must also be understood to great precision in order for CHIME to see the cosmological signal that it was built to detect. While CHIME’s cylindrical dish, radio interferometer design enables its incredible survey speed, it introduces complex instrumental effects into CHIME data. I will discuss recent work around the development of data processing procedures to model these instrumental effects and remove them from CHIME sky maps. Such work takes significant steps toward conducting Galactic science with CHIME and helps improve our understanding of the instrument.
Remote Talk: A dusty view of star formation along filaments and ionised bubbles
Pedro Palmeirim (Institute of Astrophysics and Space Sciences, Porto, Portugal)
Far-infrared (FIR) emission of interstellar dust reveals how star formation in the Milky Way is associated with filamentary structures and ionised bubbles. While filaments are the nurse beds for the large majority of stars, HII ionised bubbles generated by massive stars can influence the formation of other generations of stars. This seminar will thus focus on the relevance of these two mechanisms of forming stars. First, the importance of the role of filamentary structures in the star-formation process will be shown in highlighted results from the Herschel Gould Belt Survey. We will then look into the result of a large statistical study of ~70 000 star-forming sources (detected in Hi-GAL and GLIMPSE surveys) located in the vicinity of 1360 bubble structures and their local environments. Finally, we will look into how compression between galactic bubbles can potentially generate star-forming filaments.
Remote Talk: Wideband Cryogenic Receiver Development
Sara Salem (DAO)
The Millimetre Instrumentation Group (MIG) at NRC Herzberg in Victoria, Canada is currently developing a dual linear polarization, single-feed Q-band (35 – 50 GHz) cryogenic radio astronomy receiver with calibration noise injection designed for use both as a candidate receiver for the National Radio Astronomy Observatory’s Next Generation Very Large Array (ngVLA) and to test the high-frequency performance of the composite reflectors of Dish Verification Antenna 2 (DVA2) at NRC Herzberg in Penticton. DVA2 is a single-piece rim-supported composite materials antenna with an unblocked aperture offset Gregorian design. The Q-band receiver system is designed to achieve a receiver temperature of less than 25 K. When installed on the telescope the receiver system will consist of a cryostat with a cooled feed horn, OMT with integrated noise coupler, and low noise amplifiers with TLNA = 12 K. Following is a signal conditioning stage including filtering and amplification, and a down conversion stage. In my talk I will describe the design and current project status.
Remote Talk: Dynamic star formation
Eve J. Lee (McGill)
Star formation is a slow process on galactic size and timescales, with a mere ~2% of the gas mass turning into stars in the disk dynamical time. Is the rate of star formation uniformly small even at small scales? We cross-correlate all-sky Milky Way giant molecular clouds with star-forming complexes and show that on the cloud scale, the star formation efficiency and star formation rate per free-fall time vary widely, with a full range of about 4 orders of magnitude. Such broad distribution cannot be explained by any model that relies purely on the variance of cloud properties (e.g., virial parameter, turbulence Mach number). We show that dynamic star formation, whereby the star formation rate is explicitly time-varying, can match the observed scatter, and we present a physical understanding behind the accelerating star formation both numerically and analytically.
Remote Talk: Unravelling the magneto-ionic fabric of the Milky Way Galaxy
Alec Thomson (CSIRO)
Magnetic fields pervade the interstellar medium (ISM) of the Milky Way. These fields interact with various components within the ISM, locking-in to the ionised phases of the ISM, forming the magneto-ionic medium. This medium is responsible for a significant input of energy into the ISM. The study of magnetic fields in the ISM of the Milky Way is therefore critical to understanding the energetics and evolution of the Galaxy. I will present results of all-sky diffuse radio polarimetry made with the Parkes 64m Telescope. Considerable effort has recently been made in the observation of diffuse polarized emission across the entire sky. Polarized radio emission carries a wealth of information on the magneto-ionic medium. Linearly polarized waves experience Faraday rotation as they propagate through the magneto-ionic medium of the Milky Way. Further, the Galaxy itself is a significant source of polarized emission via synchrotron radiation. In combination with measurements of additional ISM tracers, we have used these observations to unravel the magneto-ionic properties of the Galactic ISM.
Remote Talk: Shapiro Delay-Enabled Mass Measurements of Two Notable Millisecond Pulsars
Thankful Cromartie (University of Virginia)Millisecond pulsar (MSP) timing — the process of accounting for every rotation of a rapidly spinning neutron star over long time spans — is a powerful tool for probing realms of physics that are otherwise inaccessible to Earth-based scientists. In this talk, I will discuss our use of relativistic Shapiro delay measurements to precisely determine the mass of two unique MSPs. The first, J0740+6620, is one of the 70+ MSPs timed as part of the North American Nanohertz Observatory for Gravitational Waves (NANOGrav) pulsar timing array. By combining NANOGrav observations of this source with orbital phase-specific observations near conjunction using the Green Bank Telescope (GBT), we measure the pulsar’s mass to be ~2.14 ± 0.09 solar masses. The measurement of such a massive neutron star is a significant constraint on the poorly understood neutron star equation of state (EoS). I will discuss a second targeted campaign using the GBT to measure the mass of J1231-1411, which is a source of interest for the Neutron Star Interior Composition Explorer (NICER) X-ray telescope, as well as for the Fermi Gamma-ray telescope. The joint analysis of radio and high-energy pulsar timing data is powerful in our attempt to understand pulsar astrophysics and the neutron star EoS.
Remote Talk: Dwarf Galaxies Before JWST: The Importance of Extragalactic HST UV Imaging Surveys
Anahita Alavi (Caltech)
Dwarf galaxies (M*/M0 < 109) are the smallest and least luminous, but most abundant galaxies in the universe. These galaxies are at the forefront of many important questions in galaxy formation theory, yet observationally we are only just beginning to constrain their physical properties, especially at high redshifts. Early dwarf galaxies are one of the primary targets of the next generation of telescopes including James Web Space Telescope (JWST). In this talk I will show how combination of our deep UV imaging with WFC3/UVIS camera on board the Hubble Space Telescope (HST) and extensive spectroscopic observations with MOSFIRE spectrograph at the Keck observatory allowed us to 1- observe dwarf galaxies at high redshifts (i.e., 1 < z < 3), which have always been below the detection limits of many surveys, and 2- better understand the formation and evolution of this population of galaxies via studying their number density evolution (i.e, luminosity function), star formation history (i.e., bursty SFH) and dust attenuation. In addition, I will introduce our new large UV imaging surveys with HST (UVCANDELS and UV Frontier Fields II), which will further explore the high-redshift dwarf galaxies. These UV surveys are vitally important because some of their primary science goals, such as studying the escaping ionizing radiation from galaxies, cannot fundamentally be studied by JWST. Relatedly, I will present our recent work of searching for escaping ionizing radiation from low-mass galaxies at high redshift.
Remote Talk: Characterizing Star Forming Clumps in the Galaxy: A Comparison of JCMT and Herschel Observations
Kianoosh Tahani (KPU)
We present a comparison between the Herschel Infrared Galactic plane survey (Hi-GAL) at 500 µm and the James Clerk Maxwell Telescope (JCMT) Plane Survey (JPS) using SCUBA-2 at 450 µm. The JCMT data were taken as a part of a follow up project for the JPS – circular regions with a radius of ∼ 0.8d at l = 10d & l = 30d . Given the higher resolution of the JPS 450 µm observations, we were able to determine the number of clumps identified in the Hi-GAL 500 µm data (PLW), that are actually composed of multiple, smaller clumps (i.e. the fragmentation). We investigate how Star Formation Efficiency (SFE) calculated for the monolithic Hi-GAL clumps changes when the multiplicity fraction is incorporated.
Remote Talk: Molecular clouds: Linking simulations and observations
Daniel Seifried (Cologne)
I present novel simulations of molecular cloud formation in galactic disks within the SILCC-Zoom collaboration. The simulations include as one of the first a detailed chemical network for H_2 and CO formation and thus provide a unique tool to discuss important aspects of molecular cloud formation: the (1) chemo-dynamical evolution and (2) the comparison with actual observations by means of synthetic observations. I will show that molecular clouds can be out of chemical equilibrium which provides a huge challenge for any simulations. Using the abundance information for H_2 and carbon bearing species like CO, C and C+, I investigate their line emission and the impact on the X-factor. Furthermore, in view of the increasing number of polarisation observations, I present the first self-consistent synthetic dust polarisation maps created with the POLARIS code. I will show that observed polarisation vectors in clouds probe the real field structure with an accuracy of about 5 degree and that the long-debated de-polarisation on clouds scales results from strongly tangled field lines rather than inefficient grain alignment. Finally, I will shed light on the origin of the alignment of magnetic field and density structures as currently observed by e.g. the Planck and BlastPol collaboration.
Remote Talk: The Submillimeter Array: Present and Future
David J. Wilner (CfA)
The Submillimeter Array (SMA) has pioneered submillimeter imaging and spectroscopy at subarcsecond resolution for more than 15 years with its eight 6-meter diameter antennas sited on Maunakea, Hawaii, transforming our understanding of a broad range of astrophysical phenomena such as planet-forming disks and starburst galaxies. More recently, the international Atacama Large Millimeter/submillimeter Array (ALMA) has provided an enormous leap in sensitivity and angular resolution at these wavelengths. In this talk, I will discuss the current landscape of millimeter and submillimeter telescopes, their complementarity, and how the SMA has embarked on an ambitious, staged, strategic upgrade that capitalizes on new technologies to maintain a leading role in the ALMA era. Unique capabilities already available with the SMA include 48 GHz of instantaneous bandwidth (with 139 kHz channels) in the workhorse 230 GHz and 345 GHz atmospheric windows, enabling efficient spectral line surveys, improved studies of transient phenomena, and higher overall throughput. Development towards 128 GHz of instantaneous bandwidth is underway, with a design that explicitly incorporates room to pursue future innovations aimed at new science goals. SMA observing time is available to the community on a competitive basis, with semiannual proposal deadlines for rapid response.
Remote Talk: Planetary footsteps in protoplanetary disks
Gesa H.-M. Bertrang (MPIA)
Instruments such as SPHERE and ALMA truly revolutionized our understanding of protoplanetary disks. Rings, gaps, and spirals detected by dust observations point towards embedded planets. We witnessed the first detections of such young planets just recently, and now, we are at the verge of seeing ALMA being turned into a planet hunting machine. In this talk, I will give an overview of the latest achievements in the optical and the (sub)mm and discuss future prospects of expanding these techniques to deepen our understanding of the formation of present day’s planet population.
Remote Talk: Discovery of a thirty-degree long ultraviolet arc in Ursa Major
Andrea Bracco (Rudjer Boskovic Institute, Croatia)
I will present the discovery of the Ursa Major Arc, an astonishing arc-like structure seen in the ultraviolet and extending over thirty degrees in the Northern sky with a thickness of only a few arcminutes toward the constellation of the Ursa Major. This direction of the sky is known for very low hydrogen column density and dust extinction; many deep fields for extra-galactic and cosmological investigations lie in this direction. The Ursa Major Arc enriches the complex filamentary structure of the diffuse interstellar medium in the Milky Way as recently revealed by spectroscopic and continuum observations of neutral hydrogen and dust emission, respectively. Diff use ultraviolet interstellar emission is often associated to scattering of light by interstellar dust grains. However, the lack of correlation between the Ursa Major Arc and dust emission observed with the Planck satellite suggests that other emission mechanisms must be at play. I will discuss the origin of the Ursa Major Arc as the result of an interstellar shock in the Solar neighborhood possibly related to an unknown nearby supernova remnant.
Remote Talk: Tracing the evolution of circumstellar disks with ALMA
John Carpenter (ALMA Observatory)
The supply and lifetime of gas and dust in circumstellar disks are among the primary determinants of the properties of young planetary systems. Most information on disk evolution until recently has come from infrared surveys, which have established that hot dust in primordial disks dissipates in approximately 5-10 Myr. ALMA is playing a central role in advancing demographic studies by probing the cold gas and dust in hundreds of disks contained in multiple star forming regions that span a wide range of ages. I will provide an overview of recent ALMA surveys that collectively trace the evolution in the dust content, size, and structure of circumstellar disks.
Remote Talk: Cosmic Extremes: Radio Time-Domain Astrophysics in a Multi-Messenger World
Kate Alexander (northwestern University)
Time-domain astrophysics provides a unique opportunity to study the most extreme physical processes in the Universe, including the deaths of massive stars, the creation and merger of compact objects like neutron stars and black holes, and the tidal disruption of stars by supermassive black holes. I will discuss my recent and ongoing work to reveal the formation and structure of relativistic jets and outflows in the most extreme classes of astrophysical transients, including gamma-ray bursts (GRBs) and tidal disruption events (TDEs). Radio observations of these transients are of particular interest, revealing the total energy contained in outflowing material, the magnetic field strength and geometry, and the density of the surrounding environment, which can provide clues to the progenitors of stellar explosions (GRBs) and probe models of black hole growth and accretion (TDEs). With the pioneering detections of gravitational waves, astronomers and physicists have gained a new, complementary tool to study compact object mergers and their associated GRBs, with implications for fields as wide-ranging as general relativity, nuclear physics, cosmology, and shock physics. Simultaneously, new radio interferometers like the ngVLA and the Square Kilometer Array are poised to transform radio astronomy, revealing the radio sky in unprecedented depth and leading to the discovery of relativistic transient populations in the radio band.
Remote Talk: Dynamics of streamers towards the CND – witnessed on-going mass accretion
Pei-Ying Hsieh (ALMA Observatory)
The interaction between a supermassive black hole (SMBH) and the surrounding material is of primary importance in astrophysics. The detection of the molecular 2-pc circumnuclear disk (CND) immediately around the Milky Way SMBH, SgrA*, resembles the “molecular torus” in AGNs, provides an unique opportunity to study SMBH accretion at sub-parsec scales. However, the CND is transient if its gas density is under the tidal threshold of SgrA*/nuclear star clusters, thus depleting the source of fuel. In our new CS line maps, we find several dense gas streamers appear to carry gas directly toward the nuclear region and might be captured by the central potential. These streamers show a signature of “infalling” motion with progressively higher velocities as the gas approaches the CND and finally end up co-rotating with the CND. Furthermore, utilizing the JCMT 850 um polarization data, we also find that the magnetic field appears dynamically significant toward the CND and also onwards to the inward ionized flows. Our results might suggest a possible mechanism of gas feeding to the CND. I will also talk about the observed morphology, kinematics of gas, and effects of magnetic fields in the GC. I will present our newest ALMA CS line maps in this region. As the nearest observable Galactic nucleus, this feeding process may have implications for understanding the processes in extragalactic nuclei.
Remote Talk: Early Polarization Results from the CHIME/FRB Baseband System
Ryan Mckinven (UofT)
Recent polarization measurements of Fast Radio Bursts (FRBs) offer new and exciting territory for studying these enigmatic sources. No longer limited to a relatively small sample, the triggered baseband system operating within the FRB survey of The Canadian Hydrogen Intensity Mapping Experiment (CHIME) will allow polarization analysis of hundreds of FRBs. In this talk, I summarize the automated polarization pipeline that will deliver polarized products such as rotation measures (RMs), polarization angles (PAs) and polarized fractions. I discuss how these polarized observables may constrain the nature of the population and the FRB emission mechanism/s. Finally, I report on an evolution in RM and PA in some repeating sources and compare this behaviour to similar observations from known astrophysical sources and speculate on how this may be used to constrain the nature of the source.
Remote Talk: TBD
Chentao Yang (UofT)
Submillimeter water (H2O) lines are a unique diagnostic tool of the physical conditions of the interstellar medium and properties of the radiation field in the warm dense gaseous regions of infrared-luminous galaxies. H2O is the second brightest molecular emitter in the submillimeter band after the CO lines in infrared-bright galaxies. In nearby galaxies, Herschel Space Telescope has made significant progress in studying the H2O lines, which are almost only observable from the space. In comparison, the H2O lines are readily accessible at high redshift when they are shifted into atmospheric millimeter windows, especially in the strongly lensed galaxies with current ground-based (sub)millimeter telescopes. This talk gives a brief review of the hitherto progress of the observations of the H2O lines across cosmic time based on recent NOEMA and ALMA results. The physical properties of the interstellar medium and the radiation fields inferred from the excitation of the H2O lines will also be discussed in the talk. Besides H2O, the talk also presents recent detections of H2O+ lines in a few high-redshift sources, enabling us to study the ionization state of the interstellar medium in the early universe and the formation of H2O through ionic reactions.
Remote Talk: An Optical View of Galactic Center: Ionized Gas in the Bar and
Dhanesh Krishnarao (University of Wisconsin-Madison)
Observational studies of the interstellar medium (ISM) benefit from the small scale details seen within the Milky Way and large scale trends and global characteristics seen in extragalactic samples. In the inner Galaxy, WHAM observations towards a low extinction window reveal anomalous ionization conditions traced by many optical emission lines, commonly used in extragalactic surveys, originating from the Tilted Disk, an elliptical disk of neutral gas with semi-major axis of 1.5 kpc tilted out of the Galactic plane. The atomic hydrogen in this structure is at least 48% ionized and the optical emission is characteristic of Low Ionization (Nuclear) Emission Regions (LI(N)ERs). This work demonstrates that the inner Milky Way is now the closest known example of a LI(N)ER to us in the universe and provides a new testing ground to observationally constrain the sources of ionization. This structure may interact with the Fermi Bubbles at low latitudes and WHAM observations towards a quasar sight line passing through the Fermi Bubbles reveal optical emission at the same high-negative velocity as previously discovered UV absorption. The combination of emission and absorption provide a direct measure of in-situ ionized gas conditions, suggesting that the H-alpha emitting gas comes from a thin and over-pressured zone along the Fermi Bubble shell. Ultimately, an improved understanding of the 3D distribution and kinematics of gas in both the bar and Fermi Bubbles will provide critical insight on the radiation field permeating the inner Galaxy and halo.
Remote Talk: TBD
Anna Ordog (DRAO)
Remote Talk: TBD
Ken Tapping (DRAO)
Remote Talk: TBD
Lynn D. Matthews (MIT Haystack Observatory)
Remote Talk: TBD
Valentina Vacca (Cagliari Observatory)
Remote Talk: TBD
Elizabeth Humphreys (ALMA Observatory)
Remote Talk: Application of Machine Learning to Identify Stellar Feedback
Duo Xu (University of Texas at Austin)
Stellar feedback, such as stellar winds and outflows, plays a significant role in both physical and chemical evolution of molecular clouds. This energy and momentum leave identifiable signatures (bubbles and outflows) that affect the dynamics and structure of the cloud. Most feedback feature searches are performed “by-eye”, which are usually time-consuming, subjective and difficult to calibrate. Automatic classifications based on machine learning make it possible to perform systematic, quantifiable and repeatable searches for stellar feedback features. I will first introduce a machine learning algorithm based on random forests, Brut, and quantitatively evaluate its performance in identifying bubbles using synthetic dust observations. I will show that synthetic observations combined with observational bubbles identified by citizen scientist significantly improve machine learning classification in dust emission. I will also introduce a new deep learning method CASI-3D (Convolutional Approach to Structure Identification-3D) to identify stellar feedback signatures in molecular line spectra. The CASI models are able to identify all previously identified feedback features in Taurus and Perseus, and identify new feedback structures as well. Meanwhile, the CASI models indicate that the mass, momentum and energy from feedback are overestimated by a large factor in previous studies. Consequently, feedback (bubbles+outflows) is not sufficient to support turbulence in Taurus. I will also discuss multiple astrostatistics that indicate the presence of stellar feedback in observations.
Remote Talk: TBD
Theodoros Nakos (ALMA Observatory)