Number: O1
Session: Compact Objects
Title: From the thermonuclear supernova to the supernova remnant
First Author: Gilles Ferrand
Co-authors: Gilles Ferrand, RIKEN Cluster for Pioneering Research (CPR) and Interdisciplinary Theoretical and Mathematical Sciences Program (iTHEMS); Donald Warren, RIKEN iTHEMS; Masaomi Ono, RIKEN Cluster for Pioneering Research (CPR) and iTHEMS; Shigehiro Nagataki, RIKEN CPR and iTHEMS; Friedrich K. Röpke, Zentrum für Astronomie der Universität Heidelberg, and Heidelberger Institut für Theoretische Studien (HITS); Ivo R. Seitenzahl, School of Science, University of New South Wales, Australian Defence Force Academy; Florian Lach, HITS; Hiroyoshi Iwasaki, Rikkyo University; Toshiki Sato, RIKEN
Abstract: Supernova remnants (SNRs) are the outcome of supernovae (SNe), explosions that mark the death of massive stars (core-collapse supernovae), or the second death of white dwarfs (thermonuclear supernovae). Recent progress in the simulation of SNe has shown the importance of turbulence and asymmetries in successful explosions, which prompts us to revisit the subsequent phase, the SNR phase. Can we use the SNR morphology as a probe of the explosion mechanism? The interest of this approach was demonstrated for a core-collapse SNR like Cas A. We argue for the case of a thermonuclear SNR like Tycho. We have run 3D simulations of a SNR starting from the output of 3D simulations of the thermonuclear explosion of a Chandrasekhar-mass white dwarf. By analyzing the wavefronts we can quantify the imprint of the explosion on the remnant over time. Assuming a uniform ambient medium, we find that the impact of the SN on the SNR may still be visible after hundreds of years. We will present a first comparative study of different explosions models bearing different levels of asymmetry. We will conclude on prospects for comparisons with X-ray observations of young Galactic SNRs.
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Number: O2
Session: Compact Objects
Title: Targeted sub-threshold GRB searches with BAT-GUANO
First Author: Aaron Tohuvavohu
Co-authors:
Abstract: I will present the Swift/BAT-GUANO targeted Gamma-Ray Burst (GRB) search pipeline, that links together innovative space-telescope commanding, new data taking modes, and novel analysis techniques to perform the most sensitive targeted searches for GRBs coincident with Gravitational Waves, Fast Radio Bursts, and other short duration transient events. GUANO also uniquely provides arcminute localizations for GRBs detected (but poorly localized) by other instruments, reporting ~15% of the worldwide rate of arcminute GRBs in 2020. I will discuss GUANO-enabled science to date, and outline work on extensions in progress to further the ultimate goal of prompt GW counterpart localization.
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Number: O3
Session: Compact Objects
Title: Discovery of local Universe FRBs by the CHIME/FRB Collaboration
First Author: Mohit Bhardwaj
Co-authors: CHIME/FRB Collaboration
Abstract: Fast radio bursts (FRBs) are one of the great unsolved mysteries in astronomy. Though a plethora of models has been proposed to explain FRBs, the origin of these intense millisecond-duration pulses of radio emission remains a topic of debate, largely due to the paucity of well-localized FRBs. A promising method to test the proposed FRB theories is by associating FRBs with other astronomical phenomena. By identifying their hosts and/or multiwavelength counterparts, we can narrow down potential progenitors of FRBs. Unfortunately, due to the limited sensitivity of high-energy telescopes, multi-wavelength follow-up is most promising for nearby FRBs (distance < 100 Mpc). The Canadian Hydrogen Intensity Mapping Experiment (CHIME)/FRB project has been detecting FRBs since July 2018, and many of them have sufficiently low dispersion measure (DM) suggesting a nearby origin. Even better, the localization of low-DM FRBs to a few arcminute precision using the CHIME/FRBbaseband system can result in a reliable host association. In this talk, I will report on recent CHIME/FRB discoveries of local universe FRBs, including 20200120E and 20181030A, for which we identified M81 (3.6 Mpc) and NGC 3252 (24 Mpc) as the promising hosts (if extragalactic), respectively. Lastly, I will also discuss how these localized nearby FRBs can be useful in constraining different FRB progenitor models.
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Number: O4
Session: Compact Objects
Title: Finding new pulsars with CHIME/FRB
First Author: Adam Dong
Co-authors: The CHIME Collaboration
Abstract: Pulsars are compact objects which are remnants of once-massive stars. Most act like radio frequency lighthouses and studying them has led to progress in gravitational waves and fundamental theories of physics. Ongoing research areas include the origin of pulsar emission and the irregular ways some pulsar-like objects manifest. These include intermittent pulsars who turn on like a regular pulsar for a while but remain off otherwise and Rotating Radio Transients (RRATs) which emit sporadic single pulses; usually with an underlying period. The Canadian Hydrogen Intensity Mapping Experiment (CHIME) is among the telescopes that have been commissioned to find fast radio bursts (FRB) and pulsars. This talk addresses the development and deployment of a novel pipeline for finding new pulsars from single-pulse events using the FRB detector. We employ an unsupervised machine learning algorithm on the vast astronomical database collected by the CHIME/FRB collaboration over 29 months. The process has led to 144 candidates, with at least 15 confirmed new pulsars. Many of the pulsars discovered are RRATs, adding to the relatively small sample of known examples and highlighting CHIME’s natural ability to detect and characterize these objects.
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Number: O5
Session: Compact Objects
Title: Measuring fundamental jet properties with multi-wavelength fast timing of the black hole X-ray binary MAXI J1820+070
First Author: Alexandra Tetarenko
Co-authors: P. Casella (INAF), J. Miller-Jones (ICRAR), G. Sivakoff (University of Alberta), J. Paice (University of Southampton), F. Vincentelli (University of Southampton), T. Maccarone (Texas Tech), P. Gandhi (University of Southampton), V. Dhillon (University of Sheffield), T. Marsh (University of Warwick)
Abstract: Time-domain observations now offer a promising new way to study accretion and jet physics in X-ray binaries. Through detecting and characterizing rapid flux variability in these systems across a wide range of frequency/energy bands (probing emission from different regions of the accretion flow and jet), we can measure properties that are difficult, if not impossible, to measure by traditional spectral and imaging methods (e.g., size scales, geometry, jet speeds, the sequence of events leading to jet launching). While variability studies in the X-ray bands are a staple in the X-ray binary community, there are many challenges that accompany such studies at longer wavelengths. However, with recent advances to observing techniques/instrumentation, the availability of new computational tools, and today’s improved coordination capabilities, we are no longer limited by these challenges. In this talk, I will discuss exciting new results from fast timing observations of MAXI J1820+070, where we simultaneously sample ten different wavebands (from radio through X-ray) over a range of timescales. With this work, I will highlight how we can directly connect variability properties to internal jet physics, deriving fundamental jet properties from time-series signals alone. Additionally, I will discuss future prospects for obtaining more of these invaluable fast timing data sets, and the key role that next-generation instruments will play in driving new discoveries through this science.
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Number: O6
Session: Surveys & Instruments
Title: Early Results from VERTICO: the Virgo Environment Traced in CO Survey
First Author: Toby Brown
Co-authors: The VERTICO Collaboration
Abstract: 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 data set, 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.
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Number: O7
Session: Surveys & Instruments
Title: Characterizing Exoplanets with an Imaging Fourier Transform Spectrograph
First Author: William Thompson
Co-authors: Christian Marois / NRC Herzberg, Olivier Lardière / NRC Herzberg, Ben Gerard / UC Santa Cruz, Garima Singh / NRC Herzberg
Abstract: Combining direct imaging with high resolution spectroscopy could become a powerful method for detecting and characterizing exoplanets for the 2020s and beyond. At the NRC New-Earth lab, we are developing a next generation instrument concept that combines high-speed focal plane wavefront sensing (FAST) and an imaging Fourier transform spectrograph (IFTS). This novel concept will provide diffraction limited, R~20,000 spectra over a wide field of view, and suppress starlight speckles by up to an additional factor 400×, or contrast deeper than 1×10⁻⁶ at only a few λ/D. We will present a combination of lab results and simulations to show how this level of sensitivity could allow us to detect and characterize planet atmospheric composition, orbital velocity, rotation rates, and perhaps even discover large exomoons.
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Number: O8
Session: Surveys & Instruments
Title: SIGNALS: The Star-formation, Ionized Gas, and Nebular Abundances Legacy Survey
First Author: Laurie Rousseau-Nepton
Co-authors: R. Pierre Martin, UH Hilo, Carmelle Robert, U. Laval, Laurent Drissen, U. Laval, Philippe Amram, LAM, SIGNALS collaboration
Abstract: October 2018 marked the beginning of a new large program at the Canada-France-Hawaii Telescope: SIGNALS, the Star-formation, Ionized Gas, and Nebular Abundances Legacy Survey. During the next four years and with 55 nights of telescope time in hand, our collaboration will observe almost all the extragalactic HII regions within a distance of 10 Mpc using the Imaging Fourier Transform Spectrograph (IFTS), SITELLE. The goal is to get spectral information over the strong emission lines of the visible (i.e. [OII]3727, Hbeta4861, [OIII]4959,5007, [NII]6548,6583, Halpha6563, HeI6678, [SII]6716,6731) with a spectral resolution of 5000 (on Halpha) at a mean spatial resolution of 15 parsecs. SITELLE, with its FOV of 11 arcminutes and its 4 million spaxels, is the perfect instrument for such a survey. In order to build a sample of more than 50,000 HII regions located in different galactic environments, SIGNALS will cover about 40 galaxies that are actively forming stars. Our collaboration aims at studying resolved star-formation activity, understanding the impact of the local environment on the star-formation process, and providing the science community with a unique dataset along with new tools to study star formation. During this presentation, I talk about the latest progress of the survey and show some preliminary results.
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Number: O9
Session: Surveys & Instruments
Title: Revealing asymmetrical dust distribution in the inner regions of HD 141569
First Author: Garima Singh
Co-authors: T. Bhowmik (1), A. Boccaletti (1), P. Thébault (1), Q. Kral (1), J. Milli (2), J. Mazoyer (1)et al. (including the SPHERE consortium)
Affiliations
1. LESIA, Observatoire de Paris, Université PSL, CNRS, Université de Paris, Sorbonne Université, 5 place Jules Janssen, 92195 Meudon, France
2. CNRS, IPAG, Université Grenoble Alpes, 38000 Grenoble, France
Abstract: High-contrast imaging combined with spectroscopy and polarimetry offers a pathway to study grain distribution and properties of debris disks in exquisite detail. We obtained polarimetric differential imaging of a gas-rich debris disk around HD 141569A with the SPHERE/VLT instrument in the H-band in order to compare the scattering properties of the innermost ring at 44 au with former observations in total intensity with the same instrument. In polarimetry, we observed that the intensity of the ring is peaking at the south-east, mostly in the forward direction, while in total intensity the ring is detected only at the south. This noticeable characteristic suggests a non-uniform dust density in the ring. With these two sets of images, we studied the distribution of the dust in order to solve for the actual dust distribution.
We implemented a density function varying azimuthally along the ring, and we generated synthetic images both in polarimetry and in total intensity which are compared to the actual data. We found that the dust density is peaking in the south-west at an azimuthal angle between 220-238 degree with a rather broad width between 61-127 degree. Furthermore, the location of the dust peak is consistent with the enhancement of CO measured with ALMA (Difolco et al 2020) possibly pointing to a link between the distributions of gas and dust. We concluded that the origin of this dust density distribution could be the result of a massive collision when we account for the effect of the high gas mass present in the system on the dynamics of grains. Using the outcome of our modelization, we further measured the polarized scattering phase function for the observed scattering angle between 33-147 deg and the spectral reflectance of the southern part of the ring between 0.98-2.1um. We tentatively derived grain properties by comparing these quantities with MCFOST models and assuming Mie scattering.
In this talk, I will introduce the disk structure observed within 100 AU both in total and polarimetric intensity data obtained with SPHERE. I will then present MCMC and grid-search modeling analysis followed by the results and conclusion.
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Number: O10
Session: Surveys & Instruments
Title: First weak lensing results from UNIONS
First Author: Michael Hudson
Co-authors: CFIS/UNIONS team
Abstract: The Canada-France Imaging Survey (CFIS), carried out at CFHT, is a major component of the Ultraviolet Near-Infrared Optical Northern Survey (UNIONS), which will image 5,000 square degrees of the Northern sky in 5 bands. A major scientific goal of CFIS is weak gravitational lensing. I will describe the team effort to create weak lensing shape catalogues and present first results on the ellipticity of drak matter haloes, and the dark matter halo masses of tidally-stripped galaxies in groups and clusters.
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Number: O11
Session: Gravitational Waves & Black Holes
Title: The Landscape of Disk Outflows From Black Hole – Neutron Star Mergers
First Author: Rodrigo Fernández
Co-authors: Francois Foucart (Univ of New Hampshire), Jonas Lippuner (Los Alamos Nat Lab)
Abstract: Mass ejection from accretion disks formed in mergers of black holes (BHs) and neutron stars (NSs) is a significant contributor to the production of r-process elements and to the kilonova transient. However, there has been limited exploration of the broad parameter space of disk outflows, which becomes relevant given the event rate of O3 and the lack of any detected electromagnetic counterparts. I’ll report the results of 27 high-resolution, axisymmetric, long-term viscous hydrodynamic simulations of post-merger BH accretion disks that include neutrino emission/absorption and post-processing with a nuclear reaction network. We characterize the dependence of the fraction of the disk mass ejected on disk compactness (BH mass over initial disk radius) and on the disk mass at fixed compactness. The radioactive luminosity from the disk outflow alone available to power kilonovae spans two orders of magnitude over the BH-NS parameter space. For most plausible binary configurations, this disk contribution is well below the kilonova mass upper limits for GW190814.
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Number: O12
Session: Gravitational Waves & Black Holes
Title: Gravitational Wave Backgrounds from Low Scale Inflation
First Author: Simran Nerval
Co-authors: Amit Bhoonah, Joseph Bramante, Ningqiang Song,
Abstract: While Big Bang cosmology successfully explains much of the history of our universe, there are certain features it does not explain, for example the spatial flatness and uniformity of our universe. One widely studied explanation for these features is cosmological inflation. I will discuss the gravitational wave spectra generated by inflaton field configurations oscillating after inflation for E-Model, T-Model, and additional inflationary models. I will show that these gravitational wave spectra provide access to some inflation models beyond the reach of any planned cosmic microwave background (CMB) experiments, such as LiteBIRD, Simons Observatory, and CMB-S4. Specifically, while these experiments will be able to resolve a tensor-to-scalar ratio (r) down to 10^(-3), I show that gravitational wave background measurements have the potential to probe certain inflation models for r values down to 10^(-10). Importantly, all the gravitational wave spectra from E- and T-model inflation lie in the MHz-GHz frequency range, motivating development of gravitational wave detectors in this range.
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Number: O13
Session: Gravitational Waves & Black Holes
Title: A Deep CFHT Optical Search for a Counterpart to the Possible Neutron Star Black Hole Merger GW190814
First Author: Nicholas Vieira
Co-authors: John J. Ruan, Daryl Haggard, Maria R. Drout, Melania C. Nynka, Hope Boyce, Kristine Spekkens, Samar Safi-Harb, Raymond G. Carlberg, Rodrigo Fernández, Anthony L. Piro, Niloufar Afsariardchi, Dae-Sik Moon
Abstract: The gravitational wave event GW190814 represents the first extremely high-probability merger between a compact object which may have been a neutron star and black hole. This compact binary merger was detected through gravitational waves by the LIGO/Virgo interferometers in O3. We imaged the LIGO/Virgo localization region using the MegaCam instrument on the 3.6m Canada-France-Hawaii Telescope. We describe our hybrid observing strategy of both tiling and galaxy-targeted observations to search for an electromagnetic counterpart to the event. Our observing campaign produced some of the deepest multi-band images of the region between 1.7 and 8.7 days post-merger, reaching a 5-σ depth of 22.8 in the g-band at 1.7 days and 23.1, 23.9 in the i-band at 3.7 and 8.7 days, respectively. These observations cover a mean total integrated probability of 68.8% of the localization region. We find no compelling candidate transient counterparts to this merger in our images, which suggests that either the lighter object was tidally disrupted inside of the BH’s innermost stable circular orbit, the transient lies outside of the observed sky footprint, or the lighter object belongs to a new class of low-mass black holes. We use our source detection upper limits in the NS-BH interpretation of this merger to constrain the mass of the kilonova ejecta to be < 0.015 solar masses for a ‘blue’ kilonova, and > 0.04 solar masses for a ‘red’ kilonova. Our observations emphasize the key role of large-aperture telescopes and wide-field imagers such as CFHT MegaCam in enabling deep searches for electromagnetic counterparts to gravitational wave events. These types of observations can play a leading role in the next LIGO/Virgo/KARGA observing run in 2022.
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Number: O14
Session: Gravitational Waves & Black Holes
Title: A Spectacular Multi-wavelength View of of M87 during the 2017 Event Horizon Telescope Campaign
First Author: Daryl Haggard
Co-authors: Event Horizon Telescope Multi-wavelength Working Group, Event Horizon Telescope Collaboration, Fermi-LAT Collaboration, H.E.S.S. Collaboration, MAGIC Collaboration, VERITAS Collaboration, EAVN Collaboration
Abstract: I will give an overview of the broadband multi-wavelength campaign that observed the black hole M87* alongside the Event Horizon Telescope (EHT) in 2017. The EHT’s first direct image of the centre of the M87 galaxy revealed a weakly accreting supermassive black hole with ~6.5 billion solar masses, silhouetted against the hot plasma of its accretion flow. The EHT Collaboration also partnered with international facilities in space and on the ground to launch an extensive, quasi-simultaneous multi-wavelength campaign targeting M87*. These data reveal M87* in a historically low state, both for its core as well as the nearest knot, HST-1, and represent the most complete simultaneous, multi-wavelength spectrum of the active nucleus to date. I will discuss the power and limitations of these multi-wavelength campaigns for furthering our understanding of M87*’s accretion flow and jet, and outline plans for ongoing multi-wavelength studies of M87* and Sgr A*.
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Number: O15
Session: Galaxy Evolution
Title: Kinematic Signatures of Environmental Quenching in z~0.8 Galaxy Clusters
First Author: Leo Yvonne Alcorn
Co-authors: Adam Muzzin (York University), Inger Jørgensen (Gemini Observatory), Rachel Bezanson, (U. of Pittsburgh), Arjen van der Wel (Ghent University), LEGA-C collaboration
Abstract: Environmental quenching processes are believed to impact satellite galaxies by cutting off gas accretion flows to the inflating galaxy (starvation) or rapid shock heating (ram-pressure stripping). If environmental quenching is primarily a product of starvation, gas and stellar velocity dispersion remain consistent, or if ram-pressure stripping dominates, gas velocity dispersion will be offset from stellar velocity dispersion or not detected. To investigate dynamical imprints of environmental quenching, we measure the impact of environment on the internal kinematics of galaxies as a function of environment. Our datasets consist of two highly-evolved, massive z=0.83 and z=0.89 galaxy clusters from the Gemini Cluster Project (GCP) and the environmentally-diverse Large Early Galaxy Astrophysics Census (LEGA-C) survey (0.6<z<1). We extract integrated stellar and gas velocity dispersions of the GCP clusters from GMOS-N optical spectroscopy using pPXF, in a consistent manner with LEGA-C. Additionally we utilize previously published morphological parameters from HST F775W and F814W observations of the GCP clusters, to compare to LEGA-C cluster and field samples in the Fundamental Plane and stellar and gas kinematic scaling relations. By measuring deviations from field kinematic scaling relations, and measuring stellar and gas velocity dispersion offsets, we can determine the primary causes of environmental quenching and the impacts of accretion of satellite galaxies into a galaxy cluster.
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Number: O16
Session: Galaxy Evolution
Title: Making it Big: The Effect of Dust on Galaxy Morphology
First Author: Lamiya Mowla
Co-authors: Desika Narayanan, University of Florida
Abstract: Galaxy morphology is one of the fundamental and oldest observational tools used to study the formation and evolution of galaxies. Decades of observations from the ground and thousands of orbits of extragalactic imaging by the Hubble Space Telescope (HST) have constructed a picture for the relation between the sizes and masses of galaxies, which has been used to piece together the puzzle of galaxy evolution over the last 10 Gyrs. However, it is impossible to complete this puzzle using observations alone, making cosmological hydrodynamical simulations with multi-scale models of physical processes a critical deciphering tool. Despite the success of simulations in largely matching observed galaxy scaling relations, they have yet to reproduce the observed size evolution of galaxies; the sizes of galaxies are not consistent with observations, nor across different simulations. Is this because the simulations are making galaxies with the wrong sizes? Or is it because they have not yet incorporated the effect of the major culprit that is distorting our observations of galaxies – dust? In this talk I will present the effect of dust attenuation on galaxy morphology using state-of-the-art cosmological hydrodynamical simulation SIMBA with dust radiative transfer package Powderday. If true, this might remarkably change the picture of the galaxy size-mass relation as painted by HST. Resolved stellar population synthesis modelling, augmented by upcoming JWST observation, will be needed to verify our revised view of the size-mass relation of galaxies.
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Number: O17
Session: Galaxy Evolution
Title: Galaxies in clusters are older than field galaxies at z>1: Implications for environmental vs secular quenching
First Author: Kristi Webb
Co-authors:
Abstract: Galaxies in dense clusters experience additional quenching processes compared to the secular processes which affect field galaxies. The timescale of the quenching processes can be used to constrain the physical mechanisms which suppress star formation. With the Gemini Observation of Galaxies in Rich Early Environments (GOGREEN) survey, we have collected a sample of ~300 spectra of quiescent galaxies (two-thirds of which are in clusters) at 1 < z < 1.5 — when the star formation rate was twice as high as it is today. We explore the differences of the populations, as a function of both environment and mass, through modelling their star formation histories. We confirm that in general there is mass-dependent evolution, and add to this picture that galaxies in the field have overall longer star forming time scales and are younger (at fixed mass) by ~0.3 Gyr. We try to explain this age difference through two scenarios, i) galaxies in clusters formed earlier or ii) galaxies in clusters experience environmental quenching post-infall, and find that neither are sufficient (without preprocessing) in simultaneously predicting the observed age difference and quenched fractions. This is distinctly different from local clusters, for which quenching of recently accreted field galaxies plays an important role, particularly at low stellar masses. Our results suggest that quenched population in galaxy clusters at z > 1 has been driven by different physical processes than those at play at z = 0.
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Number: O18
Session: Galaxy Evolution
Title: Tracking galaxy quenching 9Gyrs ago.
First Author: Gaël Noirot
Co-authors: Marcin Sawicki (SMU), Roberto Abraham (UToronto), Marusa Bradac (UC Davis), Gabe Brammer (Dawn), Kartheik Iyer (UToronto), Adam Muzzin (York), Camilla Pacifici (STScI), Swara Ravindranath (STScI), Chris Willott (Victoria).
Abstract: The bimodal color distribution of galaxies has been fairly well studied and characterized up to intermediate redshifts: blue galaxies have young stellar populations and are experiencing active episodes of star-formation while red galaxies are older and predominantly quenched. While it is understood that galaxies evolve from the blue to red population, constraints on their quenching timescales through the green valley in the young universe are still poor to this date.
In this talk, I will present new measurements of the full color evolution of z~1.5 galaxies (Noirot et al., in prep); a pathfinder study for future JWST programs such as CANUCS (the Canadian NIRISS Unbiased Cluster Survey). We measure the colors, ages, and galaxy star-formation histories from independent SED modelling of deep archival multi-band photometry and HST grism spectroscopy in GOODS-S and UDS. From these measurements, we derive color evolution from the blue-cloud through the green valley and to the red-sequence for rapidly quenching galaxies and their transition timescales, and estimate the growth of the red-sequence population over a period of ~2Gyrs at these redshifts.These results offer a new approach to measuring galaxy quenching over time and are consistent with the growth of the stellar mass function of quenched galaxies from the literature.
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Number: O19
Session: Cosmology
Title: The First Stars and the Birth of the Most Massive, High-redshift Quasars
First Author: Tyrone Woods
Co-authors:
Abstract: The discovery of billion-solar-mass quasars at redshift ~ 7 challenges our understanding of the early Universe — how did such massive objects form in the first billion years, and what can this tell us about their environments at Cosmic Dawn? Observations and theory increasingly favour a “heavy seed” or “direct collapse” scenario, in which the rapid accretion possible in some primordial halos leads to the formation of uniquely supermassive stars, which collapse to form the initial seeds of supermassive black holes. In this talk, I’ll present the first systematic, self-consistent simulations of the evolution of these objects under realistic formation conditions, and propose observational diagnostics to decisively test the origin of high-z quasars using next generation electromagnetic and gravitational wave observations. I’ll also discuss the expected multiplicity of such supermassive stars and their subsequent interactions, as well as the unique observational signatures of primordial stellar populations which are intermediate in mass between supermassive objects and “typical” Pop III stars in the era of JWST and beyond.
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Number: O20
Session: Cosmology
Title: Searching for dark matter in the Lyman-alpha forest
First Author: Keir Rogers
Co-authors:
Abstract: The search for dark matter offers the possibility for rich new physics that deepens our understanding of the Universe. The ultra-light axion is a compelling particle candidate that is motivated, e.g., by the string theory “axiverse” and as a possible solution to the so-called “small-scale crisis” of the cold dark matter model, if its mass is ~ 10^-22 eV. I will present new, robust bounds on the axion mass that improve by an order of magnitude over previous studies and significantly exclude the canonical mass scale of 10^-22 eV. The bounds exploit new spectroscopic observations of high-redshift (z ~ 5) quasars and absorption features formed in the intergalactic medium (IGM) — called the “Lyman-alpha forest”.
In order to address the challenge of robustly marginalising the uncertain astrophysics of the IGM, I will present a new framework for dark matter bounds using cosmological data. This utilises a novel “emulator” model for the effect of dark matter models on the power spectrum. I will discuss how the application of active learning (Bayesian emulator optimisation) can ensure robust, converged parameter inference from a limited number of expensive simulations. This is vital for accurate parameter inference from the cosmic large-scale structure, as well as other simulation-intensive problems in astronomy.
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Number: O21
Session: Cosmology
Title: Faint starlight in the brightest star-forming protocluster
First Author: Ryley Hill
Co-authors:
Abstract: Protoclusters offer us a glimpse back to the most active phase in the assembly of large-scale structure, when galaxy mergers and the ensuing star formation were at their peak. While this star formation is bright at millimetre wavelengths and easy to detect, the stars themselves are heavily obscured by dust at optical and infrared wavelengths, thus we know very little about the evolutionary state of the galaxies that make up these exciting systems. SPT2349-56 is perhaps the most extreme example, containing dozens of star-forming galaxies packed into a cubic megaparsec at z=4. We have now undertaken deep and extensive optical and infrared follow-up observations of this structure, measuring for the first time the stellar masses of a statistically significant number of z=4 protocluster galaxies. I will discuss our results, including the establishment of the galaxy main sequence in SPT2349-56, and a novel measurement of the z=4 galaxy cluster stellar mass function.
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Number: O22
Session: Cosmology
Title: A Detection of Superclustering in the Cosmic Web with ACTxDES
First Author: Martine Lokken
Co-authors: J. Richard Bond, Renee Hlozek, Alex van Engelen, Mat Madhavacheril, George Stein, Zhiqi Huang
Abstract: The Cosmic Web contains filamentary structure on a wide range of scales. On the largest scales, superclustering aligns multiple galaxy clusters via inter-cluster bridges, visible through their thermal Sunyaev-Zel’dovich signal in the Cosmic Microwave Background. We demonstrate a new way of analyzing the gas signal from these extended structures using a Compton-y map from the Atacama Cosmology Telescope combined with galaxy and cluster positions from the optical Dark Energy Survey. Clusters are oriented and stacked to align and overlay the extended signal from filaments and superclustering. We make a detection at the ~4 sigma level and find broad agreement with the Buzzard mock simulations. We highlight the promise of this novel technique for future cross-correlations of microwave and optical surveys.
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Number: O23
Session: Cosmology
Title: Finite Inflation in Curved Space
First Author: Lukas T. Hergt
Co-authors: Will J. Handley, Michael P. Hobson, Anthony N. Lasenby
Abstract: One of the many-quoted successes of cosmic inflation is its ability of naturally solving the flatness problem which states that since our Universe appears to be so close to flat today, it must have been even closer to flatness in the past. Despite this original motivator, in numerical analyses the spatial curvature is commonly neglected and set to exact flatness from the get-go to reduce the complexity of computations.
I have investigated the interdependence of cosmic inflation and spatial curvature, applying Bayesian methods to data from the Planck satellite. Even just a small amount of spatial curvature today can place significant restrictions on the duration of cosmic inflation which might be observable on the largest observable scales.
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Number: O24
Session: Star & Planet Formation
Title: Self-sustaining vortices: a mechanism for planetary system formation
First Author: Kundan Kadam
Co-authors: Zsolt Regály, Cornelis Dullemond
Abstract: The origins of our solar system as well as the diversity of observed exoplanet systems is still an open question. In particular, how the submicron sized dust particles overcome the traditional growth barriers to become planetesimals within the protoplanetary disks is not well understood. In this presentation, I will talk about our latest findings which point towards a new paradigm of planetary system formation. The dust grains present in the early disk can adsorb the charged particles and reduce the gas conductivity in their vicinity. This in turn can weaken the magnetorotational instability, which is considered to be the primary source of turbulence. With the help of numerical hydrodynamic simulations, which include dust-dependent viscosity as well as coupled gas-dust evolution, we found that a dusty protoplanetary disk can develop a cascade of self-sustaining Rossby vortices. These small-scale vortices collect large amounts of dust and are secularly stable. The local conditions within the vortices offer favorable sites for dust growth and planetesimal formation. The phenomenon of self-sustaining vortices suggests the tantalizing idea of rapid formation of planetary cores in-situ, while also being consistent with several constraints put forward by recent observations.
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Number: O25
Session: Star & Planet Formation
Title: Dust-depleted Inner Disks in a Large Sample of Transition Disks through Long-baseline ALMA Observations
First Author: Logan Francis
Co-authors: Nienke van der Marel (Banting Fellow, University of Victoria)
Abstract: Transition disks with large inner dust cavities are thought to host massive companions. However, the disk structure inside the companion orbit and how material flows toward an actively accreting star remain unclear. We present a high-resolution continuum study of inner disks in the cavities of 38 transition disks. Measurements of the dust mass from archival Atacama Large Millimeter/Submillimeter Array observations are combined with stellar properties and spectral energy distributions to assemble a detailed picture of the inner disk. An inner dust disk is detected in 18 of 38 disks in our sample. Of the 14 resolved disks, 8 are significantly misaligned with the outer disk. The near- infrared excess is uncorrelated with the mm-dust mass of the inner disk. The size–luminosity correlation known for protoplanetary disks is recovered for the inner disks as well, consistent with radial drift. The inner disks are depleted in dust relative to the outer disk, and their dust mass is uncorrelated with the accretion rates. This is interpreted as the result of radial drift and trapping by planets in a low α (∼10^-3) disk, or a failure of the α-disk model to describe angular momentum transport and accretion. The only disk in our sample with confirmed planets in the gap, PDS 70, has an inner disk with a significantly larger radius and lower inferred gas-to-dust ratio than other disks in the sample. We hypothesize that these inner disk properties and the detection of planets are due to the gap having only been opened recently by young, actively accreting planets. Unified
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Number: O26
Session: Star & Planet Formation
Title: Dynamical formation and destruction of binaries during star cluster formation
First Author: Claude Cournoyer-Cloutier
Co-authors: Aaron Tran (Columbia University), Sean Lewis (Drexel University), William E. Harris (McMaster University), Mordecai-Mark Mac Low (American Museum of Natural History, Drexel University, Center for Computational Astrophysics, Columbia University), Stephen L. W. McMillan (Drexel University), Simon Portegies Zwart (Leiden Observatory), Alison Sills (McMaster University)
Abstract: Stars are preferentially formed in clustered environments and in binary systems. Binaries are also formed and destroyed by dynamical interactions between stars in dense stellar environments, such as embedded clusters. The properties of binary populations are, therefore, set by the physics of binary formation and then modified by subsequent dynamical interactions, but the relative importance of each process is currently unknown. The first step to address this question is to determine if, and how, dynamical interactions during clustered star formation modify the statistical properties of an initial population of binary star systems, such as the mass-dependent binary fraction and the distributions of orbital properties.
We implement a realistic, field-like initial population of binaries in the coupled hydrodynamics and direct N-body star cluster formation code Torch. We compare the statistical properties of binary systems present a few Myr after the onset of star formation in simulations with, and without, our initial population of binaries. The final populations in the two suites of simulations are different both from each other and from the initial population, which indicates that primordial formation and dynamical interactions both contribute to shaping the population of binary star systems observed in the Galactic field, as well as in open and globular clusters. We summarize here the key conclusions from our first published suites of simulations and present new results.
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Number: O27
Session: Star & Planet Formation
Title: Investigating Star Formation Suppression in Galaxy Bulges with SITELLE and ALMA
First Author: Anan Lu
Co-authors: Hope Boyce (McGill University), Prof. Daryl Haggard (McGill University), Prof. Martin Bureau (University of Oxford), Dr. Timothy Davis (Cardiff University), Mark Smith(University of Oxford), Eve North (Cardiff University), Kyoko Onishi (Chalmers University of Technology), Dr. Marc Sarzi, Dr. Federico Lelli (Cardiff University), Dr. Laurie R-Nepton (Canada-France-Hawaii Telescope), Prof. Carmelle Robert (Université Laval), Thomas Martin (Université Laval), Michele Cappellari (University of Oxford), Lijie Liu (University of Oxford)
Abstract: The physics that regulates star formation is fundamental to the building of our Universe. Star formation efficiency (SFE) has been shown to vary between starbursts and deep in the bulges of galaxies. To disentangle the different mechanisms proposed to explain the suppression of star formation throughout galactic environments, observations of both ionized and cold gas with sufficient spatial resolution are vital. We have selected a sample of five spiral galaxies and five early-type galaxies that have high-resolution CO maps from ALMA, and have requested complementary observations with the imaging Fourier transform spectrometer SITELLE on CFHT to trace star-formation and gas kinematics with H-alpha. In this talk, we will present preliminary results of the SFE on a sub-kpc scale for one of our targets, NGC 3169, and provide an overview of the project.
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Number: O28
Session: Star & Planet Formation
Title: A direct link between disk structures and exoplanet demographics
First Author: Nienke van der Marel
Co-authors:
Abstract: Structures such as gaps and rings in observations of protoplanetary disks have long been hailed as signposts of planet formation. However, a direct link between exoplanets and protoplanetary disks remains hard to identify. I will present a large sample study of ALMA dust disk surveys of nearby star-forming regions in order to disentangle this connection at a statistical level. All disks are classified as either gapped or non-gapped (compact) disks. A comparison across ages reveals that gapped disks retain high dust masses up to at least 10 Myr, whereas the dust mass of non-gapped disks decreases rapidly over time. This decrease can be understood if the dust mass evolves primarily by radial drift, unless drift is prevented by pressure bumps in gapped disks. We identify a stellar-mass dependence of the fraction of gapped disks. We propose a scenario linking this dependence with that of giant exoplanet occurrence rates. We show that there are enough exoplanets to account for the observed disk structures if gapped disks are caused by exoplanets more massive than Neptune, under the assumption that most of those planets eventually migrate inwards. On the other hand, the known anti-correlation between transiting super-Earths and stellar mass implies those planets must form in the compact disks, consistent with those exoplanets forming through pebble accretion in drift-dominated disks. These findings support an evolutionary scenario where the early formation of giant planets determines the dust disk evolution and its observational appearance.
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Number: O29
Session: Exoplanets
Title: First Detection of Candidate Exoplanets and Brown Dwarfs Orbiting X-Ray Binaries via Direct Imaging
First Author: Myriam Prasow-Émond
Co-authors: Julie Hlavacek-Larrondo (Université de Montréal), Kevin Forgarty (Caltech), Julien Rameau (Université de Grenoble), Louis-Simon Guité (Université de Montréal), Dimitri Mawet (Caltech), Jack Steiner (Cfa), Andrew Fabian (Cambridge), Dom Walton (Cambridge), Lauren Weiss (University of Hawai’i), David Lafrenière (Université de Montréal), René Doyon (Université de Montréal), Étienne Artigau (Université de Montréal), Marie-Eve Naud (Université de Montréal), Anjali Rao (University of Southampton), Poshak Ghandi (University of Southampton), Carter Rhea (Université de Montréal), Théophile Bégin (Université de Montréal), Benjamin Vigneron (Université de Montréal), and Olivier Cardinal (University of Toronto).
Abstract: X-ray binaries provide fantastic laboratories for understanding the physics of matter under the most extreme conditions. However, there are currently no observational constraints on the AU-size environments of these extreme systems and it remains unclear how the accretion onto the compact objects or the explosions giving rise to the compact objects interact with their immediate surroundings. Here, we present the first high-contrast adaptive optics images of X-ray binaries aiming to probe a variety of phenomena from protoplanetary discs, to debris discs and fallback discs, as well as orbiting planetary companions. These observations target all X-ray binaries within ≈2 kpc accessible with NIRC2 on KECK. We present key results from this campaign, including the discovery of candidate brown dwarfs and exoplanets orbiting the Gamma-Cassiopeiae analog X-ray binary RX J1744.7-2713. Our talk emphasizes that such observations may indeed provide a major breakthrough in the field, not only for our understanding of the circumbinary environment of X-ray binaries, but also our understanding of how discs and planets can form even in the most extreme environments.
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Number: O30
Session: Exoplanets
Title: WASP-107b’s density is even lower: a case study for the physics of planetary gas envelope accretion and orbital migration
First Author: Caroline Piaulet
Co-authors: B. Benneke (UdeM, CA), R. A. Rubenzahl (California Institute of Technology, US), A.W. Howard (California Institute of Technology, US), E. J. Lee (McGill, CA), D. Thorngren (UdeM, CA), R. Angus (American Museum of Natural History/Flatiron Institute, US), M. Peterson (UdeM, CA), J.E. Schlieder (NASA Goddard Space Flight Center, US), M. Werner (California Institute of Technology, US), L. Kreidberg (MPIA, Germany), T. Jaouni (U of Ottawa, CA), I. J. M. Crossfield (U of Kansas, US), D. R. Ciardi (California Institute of Technology, US), E. A. Petigura (UCLA, US), J. Livingston (U of Tokyo, Japan), C. D. Dressing (U of California Berkeley, US), B. J. Fulton (California Institute of Technology, US), C. Beichman (California Institute of Technology, US), J. L. Christiansen (California Institute of Technology, US), V. Gorjian (California Institute of Technology, US), K. K. Hardegree-Ullman (California Institute of Technology, US), J. Krick (California Institute of Technology, US), E. Sinukoff (California Institute of Technology and University of Hawaii at Manoa, US)
Abstract: With a mass in the Neptune regime and a radius of Jupiter, WASP-107b presents a challenge to planet formation theories while standing out as one of the most favorable targets for atmospheric characterization. I will present the results of an extensive 4-yr Keck/HIRES radial-velocity (RV) follow-up program of the WASP-107 system, which led to a detailed study of the physics governing the accretion of the gas envelope of WASP-107b. We find that WASP-107b’s mass is of only 1.8 Neptune masses. The resulting extraordinarily low density suggests that WASP-107b’s core, while having a mass of <4.6 Mearth, accreted over five times its mass in gas while being significantly lighter than what is traditionally assumed necessary to trigger massive gas envelope accretion. We propose a new scenario for the formation of giant exoplanets consistent with the observations for WASP-107b, where the onset of accretion occurs at large orbital distances onto a low-opacity atmosphere. The observation of WASP-107b on its present-day close-in orbit could be explained by recent migration, plausibly involving WASP-107c, a 0.36 Mjup planet on a wide eccentric orbit discovered in the RV data. Overall, our new RV observations and envelope accretion modeling provide crucial insights into the intriguing nature of WASP-107b and the system’s formation history. Looking ahead, WASP-107b will be a keystone planet to understand the physics of gas envelope accretion.
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Number: O31
Session: Exoplanets
Title: Indigenizing the Drake Equation
First Author: Hilding Neilson
Co-authors:
Abstract: The famous Drake Equation is a compelling thought experiment that attempts to quantify the possible number of civilizations in the Galaxy that we might be able to communicate with. But, this equation is built on a number of assumptions that are derived from the perspective of western Eurocentric cultures and knowledges. In this talk, I discuss Indigenous methodologies for understanding nature and apply them to the Drake Equation. I show that from Indigenous perspectives the Drake Equation can predict far more civilizations in our Galaxy. I conclude with a discussion of how this result might suggest a new resolution to the historical Fermi Paradox.
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Number: O32
Session: Exoplanets
Title: Biogenic Worlds: From atmospheric HCN production to the building blocks of RNA in warm little ponds
First Author: Ben K. D. Pearce
Co-authors: Karan Molaverdikhani, Ralph Pudritz, Thomas Henning, Kaitlin Cerrillo
Abstract: An atmosphere rich in HCN is a distinguishing feature of what we term biogenic worlds. These are worlds capable of producing key biomolecules for the emergence of life rather than requiring they be delivered, e.g., by meteorites. 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 Gya (giga-years ago) and 4.0 Gya, which differ in composition, luminosity, UV intensity, and impact bombardment rate. At 4.4 Gya, UV intensity was high due to the active newly formed Sun, and asteroids and comets were bombarding the planet at an overwhelming rate of 1×10^15 kg/yr. Impact degassing at this time produced a reducing, H2-dominant atmosphere. At 4.0 Gya, the atmosphere was depleted in hydrogen due to escape from the upper atmosphere, and volcanic outgassing led to an CO2-dominant world. At steady state for both epochs, we find that HCN rainout from the troposphere leads to RNA building block production in ponds that is comparable in concentration to what would result from meteoritic delivery (ppb–ppm range). Unlike the RNA building blocks delivered by meteorites, which survive for less than a few years, the concentrations produced in situ are maintained indefinitely for both epochs due to the steady influx of HCN from the troposphere. These results suggest that early Earth was biogenic throughout both the reducing (H2-dominant) and oxidizing (CO2-dominant) phases of the Hadean eon.
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Number: O33
Session: Exoplanets
Title: Detection of a hot day side on the sub-Neptune TOI-824 b : a possibly stripped Neptune mantle
First Author: Pierre-Alexis Roy
Co-authors: Björn Benneke, Institute for Research on Exoplanets (IREx)
Abstract: The Kepler mission has shown that small planets and sub-Neptunes are more abundant in our surveys than giant planets. However, the presence of atmospheric clouds obscuring transmission spectroscopy data sets along with the fact that there is no sub-Neptune in our solar system have largely limited our understanding of the formation and properties of sub-Neptunes. The recent discovery of the hot 2.9 Earth radii sub-Neptune TOI-824 b represents a prime opportunity to change this. With its high mass and high density (almost twice as dense as Neptune), TOI-824 b’s properties are consistent with multiple bulk compositions and formation scenarios and make it a highly intriguing target. Indeed, the properties of TOI-824 b could be explained by a Neptune-like planet which formed beyond the ice line, and lost its hydrogen atmosphere during a migration period, leaving an exposed Neptune mantle. However, TOI-824 b’s properties could also be explained by a massive rocky planet which formed closer to the star and was able to accrete a large hydrogen envelope. Here, we present our analysis of the possible interior compositions of TOI-824 b along with our detection of the secondary eclipses of the planet at 3.6 and 4.5 microns with the Spitzer Space Telescope. The secondary eclipse spectrum we obtained reveals that TOI-824 b has a hot day side temperature, as both eclipse measurements are deeper than expected by the zero-albedo equilibrium temperature of the planet. These measurements allow us to identify a poor heat transport in the atmosphere of TOI-824 b. This poor heat redistribution could be explained by a dense and high metallicity atmosphere and thus be consistent with TOI-824 b being a stripped Neptune mantle, the remnant of a Neptune-like planet which lost its outer hydrogen layer. With its hot day side temperature, TOI-824 b strikes out as a prime target for further emission spectroscopy observations and might be the first evidence of a stripped Neptune mantle.
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Number: O34
Session: Exoplanets
Title: Measuring Earth’s surface temperature over geologic time.
First Author: Norman Murray
Co-authors: Hanbo Wu, Kristen Menou, Christopher Lee, Jeremy Leconte
Abstract: It is well known that the length of day is increasing, a result of Lunar and Solar tides, implying that the day was shorter in the distant pass. Geologic data confirm that in fact the day was much shorter, about 15 hours, 3 Gya. However the same data show that length of day was roughly constant, at about 19 hours, between 2 Gya and 1 Gya. This is consistent with a balance between the Lunar tidal torque and the resonant solar thermal atmospheric torque. We use the data to infer the mean surface temperature T as a function of time; a resonant atmospheric period of 19.5 hours corresponds to T = 50 C. Similarly high temperatures are reached for plausible atmospheric pressures and compositions, despite the lower Solar flux at that epoch.
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Number: O35
Session: Nearby Galaxies
Title: Deep H-alpha imaging of the M81 group: Giant clouds and fountains of gas
First Author: Deborah Lokhorst
Co-authors: Roberto Abraham, Pieter van Dokkum, Seery Chen, Imad Pasha
Abstract: The M81 group is one of the most studied interacting groups of galaxies in the local Universe, containing both a classical spiral (M81) and an energetic starburst galaxy (M82). It is therefore the perfect laboratory to look for extended ionized gas, particularly inflows and outflows to the circumgalactic medium. With a novel ultra-narrow bandpass imaging upgrade on the Dragonfly Telephoto Array, we have carried out uniquely deep H-alpha and [NII] imaging of the M81 group. Our observations have revealed a multitude of ionized gaseous features, including a colossal shell of ionized gas at the virial radius of M82, which could be circumgalactic gas streaming in for the first time or gas blown out from the M82 starburst. In addition, our observations suggest a quintessential galactic fountain in M82 and extended ionized gas linking M81 and M82. We present these discoveries and discuss their origins and implications for the feedback cycle of gas between the galaxies and the circumgalactic medium.
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Number: O36
Session: Nearby Galaxies
Title: Resolving cold circumgalactic gas in Romulus Simulations
First Author: Vida Saeedzadeh
Co-authors: Arif Babul, University of Victoria
Abstract: We use the high-resolution ROMULUS cosmological simulations to explore the properties and origin of cold circumgalactic medium (CGM) gas around massive galaxies in galaxy groups and clusters. We find that the CGM in these simulations is multiphase and dynamic, with a wide spectrum of largely nonlinear density perturbations sourced most dominantly by satellite galaxies wakes. We investigate the origin of the multiphase structure of the CGM with a particle tracking analysis and find three different effects going on in the low entropy gas. 1) low entropy gas that has cooled by cooling flow, 2) low entropy gas that has cooled from the hot halo as a result of thermal instability triggered by strong perturbations which will cool rapidly and precipitate 3) low entropy gas that has cooled from the hot halo as a result of thermal instability triggered by weak perturbations which will cool but then bounce back to its previous thermodynamic stage. We also investigate the thermodynamic history of cold gas stripped from the satellite galaxies and find that most of this gas will heat up and mix with the ICM and just a small fraction of it will continue cooling.
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Number: O37
Session: Nearby Galaxies
Title: The global and spatially resolved effects of galaxy mergers on star formation and metallicities in IllustrisTNG
First Author: Maan Hani
Co-authors:
Abstract: Galaxy scaling relations (e.g., mass metallicity relation, Kennicutt-Schmidt) have been key to our understanding of star formation and stellar feedback. In recent years, using statistical galaxy samples, IFU surveys have shown that these relations extend down to kpc and sub-kpc scales. Unlike observational studies, numerical simulations have not explored the emergence and evolution of resolved relations extensively; namely, the resolved SFMS and resolved mass metallicity relation. Moreover, our understanding of how galaxy mergers, a major evolutionary process, influence the resolved relations remains limited. By generating mock IFU data from Illustris-TNG, I present an analysis of the resolved properties of 1855 post-merger galaxies. I measure offsets of resolved regions from the resolved scaling relations to demonstrate how mergers impact galaxy properties. I demonstrate that merger-induced star formation enhancements (0.5dex) are centrally peaked, while star formation is suppressed (-0.13dex) in the outskirts (r>0.8 r_e). On the other hand, metallicities are diluted by as much as -0.1dex out to several r_e in post-mergers.These effects of the mergers on star formation and metallicity persist for several Gyr. Although galaxy mergers have a strong effect on the galaxy’s star formation and metallicity, the extent and level of the merger-induced effects depend on the galaxy properties (e.g., mass ratio, gas fraction). Compared to similarly star-forming galaxies, galaxy mergers exhibit stronger central boosts in star formation, stronger suppressions of star formation in the outskirts, and global metallicity suppressions. This difference suggests that the dynamical properties of galaxy mergers drive a unique evolutionary path for galaxies.
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Number: O38
Session: Nearby Galaxies
Title: BESPOKE Galaxy Samples: A new way to study the ISM in galaxy simulations
First Author: Samantha Benincasa
Co-authors: James Wadsley (McMaster University), Alex Pettit (Hokkaido University), Adam Leroy (the Ohio State University), Jiayi Sun (the Ohio State University)
Abstract: The nature of star formation in the galactic context remains a key unsolved area in astrophysics: it is critical for both our understanding of star formation in its own right and our understanding of the fundamental building blocks of galaxy formation. With a growing compendium of high quality observational data, now is the time to explore how the physics of star formation operates on galactic and sub-kpc scales. Major new programs with ALMA, HST and optical IFUs are providing high-resolution observations of dense gas, star clusters and star formation for galaxies spanning the star-forming main sequence. In order to contextualize these observational studies, there is a deep need for comparable theoretical work. In particular, commensurate samples of simulated galaxies are needed. In this talk, I will discuss the first results from the BESPOKE (Better Extragalactic Simulation Physics on Known Examples) project where we have created a survey of galaxies that structurally match galaxies in the THINGS and PHANGS survey samples. In this way we are are able to undertake studies of the ISM and star formation in ways that have been impossible to this point: with matched initial conditions we are able to truly understand the impacts of feedback and star formation in the ISM, as well as better constrain the assumptions in converting observed to physical quantities.
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Number: O39
Session: Nearby Galaxies
Title: Searching for Signatures of Extended Structures in the Milky Way’s Dwarf Galaxy Satellites
First Author: Jaclyn Jensen
Co-authors:
Abstract: It is currently unknown just how extended the stellar components of dwarf galaxies are, but any stars that can be found at large distances from the center of the dwarf are valuable (and rare) tracers of the dwarf’s dynamics in these low acceleration regimes. Each satellite submerged in the Galaxy’ s potential is subject to tidal forces that may cause stars to move to large distances, but it is also possible that ancient interactions between the dwarf and other small systems may have deposited stars in the far outskirts of the dwarfs (i.e., dwarf-dwarf mergers). In this work, we seek to probe the Galaxy’s satellite systems to identify extended halos around dwarfs and/or possible signs of tidal disruption caused by the Milky Way. Using the most recent Gaia data release (EDR3) and a maximum likelihood approach allowing for multi-component structures, we examine all ~60 dwarf galaxy satellites to identify candidate member stars whose positions, proper motions (with respect to the satellite’s systemic proper motion), and color-magnitudes are consistent with them being distant members of these faint systems. These rare stars are interesting beacons to help constrain the satellite’s dynamical interactions with the Galaxy, and in some cases with even smaller, since merged, stellar systems.
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Number: O40
Session: Nearby Galaxies
Title: Cool, Luminous, and Highly Variable Stars in the Magellanic Clouds from ASAS-SN: Implications for Thorne-Żytkow Objects and Super-asymptotic Giant Branch Stars
First Author: Anna O’Grady
Co-authors: Maria Drout (University of Toronto, Carnegie Observatories), B. J. Shappee (University of Hawaii), Evan B. Bauer (Kavli Institute for Theoretical Physics), Jim Fuller (TAPIR, California Institute of Technology), C. S. Kochanek (Center for Cosmology and Astroparticle Physics, University of Ohio), T. Jayasinghe (Center for Cosmology and Astroparticle Physics, University of Ohio), B. M. Gaensler (Dunlap Institute, University of Toronto), K. Z. Stanek (Center for Cosmology and Astroparticle Physics, University of Ohio), Thomas W.-S. Holoien (Carnegie Observatories), J. L Prieto (Universidad Diego Portales, Millennium Institute of Astrophysics), Todd A. Thompson (Center for Cosmology and Astroparticle Physics, University of Ohio)
Abstract: In this talk, I present the results of a systematic search for cool and luminous stars in the Magellanic Clouds with extreme variability, motivated by the properties of the unusual Small Magellanic Cloud star and Thorne-Żytkow Object (TŻO) candidate HV2112. Using light curves from the All-Sky Automated Survey for Supernovae, we identified 10 stars with surface temperatures T < 4800 K, luminosities log(L/L☉) > 4.3, variability periods >400 days, variability amplitudes ∆V > 2.5 mag, and a similar light-curve morphology to that of HV2112. We used the pulsation properties, derived occurrence rates, and comparisons to stellar populations and models to contain the nature of these 11 objects, including HV2112. Most importantly, we estimated current masses of ∼5-10 M☉, below the theoretical minimum mass of ∼15 M☉ required for TŻOs to be stable, casting doubt on this interpretation. Instead, we found that the photometric, variability, and derived physical properties of these stars are consistent with predictions for super-asymptotic giant branch (s-AGB) stars. If confirmed, these objects would represent the first identified population of s-AGB stars, illuminating the transition between low- and high-mass stellar evolution.
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