Scientific Organization Committee (SOC) · Tran Thanh Van (Rencontres du Vietnam) Nguyen Thi Minh...

Elisabete de Gouveia Dal Pino (Universidade de Sao Paulo, Brasil)

Edith Falgarone (Ecole Normale Supérieure, Paris, France)

Thiem Hoang (Korea Astronomy and Space Science Institute)

Dongsu Ryu (Ulsan Institute of Science and Technology, Korea)

Alex Lazarian (University of Wisconsin-Madison, USA)

Christopher McKee (University of California, Berkeley, USA)

Ralph Pudritz (McMaster University, Canada)

Shu-ichiro Inutsuka (Nagoya University, Japan)

Scientific Organization Committee (SOC)

Tran Thanh Van (Rencontres du Vietnam)

Nguyen Thi Minh Phuong (Quy Nhon University, Vietnam)

Local Organization Committee (LOC)

Tran Thanh Son (ICISE, Vietnam)

Le Ngoc Tram (SOFIA-USRA, USA & USTH, Vietnam)

Table of Contents

Scientific Program ••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• i – iv

Abstract Day 1 ••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• 1

Measurements and Techniques to study Magnetic Fields ••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• 1

MHD turbulence •••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• 4

Abstract Day 2 ••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• 6

MHD turbulence (continued) ••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• 6

Magnetic Fields in Interstellar Medium ••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• 9

Abstract Day 3 ••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• 12

Magnetic Fields in Interstellar Medium (continued) •••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• 12

Abstract Day 4 ••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• 15

Magnetic Fields in Interstellar Medium (continued) •••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• 15

Magnetic Fields in Compact Sources and Cosmic-ray Acceleration ••••••••••••••••••••••••••••••••••••••••••••••• 16

Magnetic Fields in Intergalactic Medium and Clusters of Galaxies ••••••••••••••••••••••••••••••••••••••••••••••••• 20

Abstract Day 5 ••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• 22

Magnetic Fields in Intergalactic Medium and Clusters of Galaxies (continued) •••••••••••••••••••••••••••••••••• 22

Poster Abstract ••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• A

Committee members •••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• F

MFU7 i

PROGRAM MFU7 Monday, Feb 17, 2020

– 08:30 Registration 08:30 – 08:45 Opening Remark

Measurements and Techniques to study Magnetic Fields

Chair : Alexandre Lazarian

08:45 – 09:15 Alexandre Lazarian Gradient Technique: New Way of Magnetic Field Studies

09:15 – 09:45 Thiem Hoang Grain Alignment Mechanisms: Current Status and Perspectives

09:45 – 10:00 Hyeseung Lee Dust polarization by radiative torque alignment and disruption

10:00 – 10:15 Chau Giang Nguyen Time-Varying Extinction, Polarization, and Colors of Type Ia Supernovae due to Rotational Disruption of Dust Grains

10:15 – 10:30 Aris Tritsis Halo's Magnetic field as Evident from Striated Interstellar Clouds (HOMERIC)

10:30 – 11:00 Coffee Break

11:00 – 11:30 Cameron Van Eck Galactic Faraday tomography at low frequencies

11:30 – 12:00 Marijke Haverkorn Probing interstellar magnetic fields with radio and optical polarimetry

12:00 – 13:30 Lunch & Beach MHD turbulence

Chair : Hyesung Kang

13:30 – 14:00 Jungyeon Cho Driving Issues in Compressible MHD Turbulence

14:00 – 14:30 Jeonghoon Lim Decay of Turbulence in Fluids with Polytropic Equations of State

14:30 – 14:45 Edith Falgarone Extrema of dissipation in MHD turbulence

14:45 – 15:15 Huirong Yan Cosmic compass - First detection of an outer 3D sub-Gauss field via atomic alignment


15:45 – 16:15 Axel Brandenburg Reversed dynamo, reversed helicity, and diagnosing it

16:15 – 16:45 Philip Mocz Studying Dense Structures in a Turbulent Interstellar Medium with a Moving Mesh

16:45 – 17:15 Discussion

MFU7 ii

PROGRAM MFU7 Tuesday, Feb 18, 2020

Chair : Marijke Haverkorn

08:30 – 09:00 Ethan Vishniac

09:00 – 09:30 Grzegorz kowal Kelvin-Helmholtz versus Tearing Instability: What Drives Turbulence in Stochastic Reconnection?

09:30 – 10:00 Joerg Buechner Turbulent magnetic reconnection in the kinetic regime

10:00 – 10:30 Siyao Xu Turbulent dynamo in diverse astrophysical media


11:00 – 11:45 Poster Presentation

11:45 – 12:00 Photo

12:10 – 13:30 Lunch & Beach Magnetic Fields in Interstellar Medium

Chair : Gianfranco Brunetti

13:30 – 14:00 Ray Furuya The JCMT BISTRO survey: submillimeter polarization spectra of thermal emission from dust grains in high-density star-forming gas

14:00 – 14:30 Katherine Pattle Magnetic fields and star formation in the Ophiuchus Molecular Cloud

14:30 – 15:00 Mehrnoosh Tahani Magnetic Fields Associated with Molecular Clouds; A New Probing Technique

15:00 – 15:15 Devaraj Rangaswamy Magnetic field in S235 complex

15:15 – 15:45 Coffee Break 15:45 – 16:15 Reinaldo Santos De

Lima On the transport and diffusion of magnetic fields in star formation

16:15 – 16:30 Kazunari Iwasaki Molecular Cloud Formation by Compression of Two-phase Atomic Gases

16:30 – 16:45 Tung Ngo Duy Rotational Disruption and Desorption of Icy Grains in Protoplanetary Disks and Implications for Snowline and COMs

16:45 – 17:15 Discussion

MFU7 iii

PROGRAM MFU7 Wednesday, Feb 19, 2020

Chair : Tsuyoshi Inoue

08:30 – 09:00 Shu-Ichiro Inutsuka The role of magnetic field in the filament paradigm of star formation

09:00 – 09:30 Yusuke Tsukamoto Impact of magnetic field on circumstellar disk formation

09:30 – 10:00 Chin-Fei Lee Magnetic Field Morphology in two Protostellar disks, a Pseudodisk, and a Protostellar jet

10:00 – 10:30 Woojin Kwon Highly Pinched Magnetic Fields of the Class 0 Young Stellar Object L1448 IRS 2


11:00 – 11:30 Xuening Bai Magnetically-controlled Gas Dynamics in Protoplanetary Disks

11:30 – 11:45 Tom Ray Measuring Magnetic Fields in the Disks and Outflows of Young Stars

11:45 – 12:00 Thi Phuong Nguyen Gas properties and dynamics from the cavity to the outer disk of GG Tau A

12:00 – Lunch & Excursion

MFU7 iv

PROGRAM MFU7 Thursday, Feb 20, 2020

Magnetic Fields in Compact Sources and CR Acceleration

Chair : Dongsu Ryu

08:30 – 09:00 Elisabete de Gouveia Dal Pino

Magnetic Reconnection Acceleration: what we have learned so far from MHD simulations with test particles

09:00 – 09:15 Juan Carlos Rodriguez-Ramirez Gamma-ray emission from magnetised, black-hole accretion flows

09:15 – 09:30 Barnali Das Coherent radio emission from hot magnetic stars: What does it tell us?

09:30 – 09:45 Jaroslaw Dyks Finding pulsar magnetosphere geometry from radio polarization data

09:45 – 10:15 Anatoly Spitkovsky Magnetic field generation and particle acceleration in shocks

10:15 – 10:30 Ngoc Tram Le Supernova Shocks in Molecular Clouds: Velocity Distribution, Combining Dynamics and Excitation of Molecular Hydrogen


11:00 – 11:30 Tsuyoshi Inoue Magnetic Field Amplification by Bell's Cosmic-ray Streaming Instability in Supernova Remnants

11:30 – 11:45 Ke-Jung Chen Magnetar-powered Supernovae

11:45 – 12:00 Andrew Lehmann UV self-irradiated molecular shocks: probing turbulent cascades in external galaxies

Magnetic Fields in Intergalactic Medium and Clusters of Galaxies

12:00 – 13:30 Lunch & Beach Chair : Elisabete de Gouveia Dal Pino

13:30 – 14:00 Marcus Bruggen Probing intergalactic fields with polarisation observations

14:00 – 14:15 Hyesung Kang Cosmic Ray Acceleration in Weak Shocks in Intracluster Medium

14:15 – 14:30 Michal Hanasz Modeling CR electron propagation and synchrotron emission from CR-driven dynamo in spiral galaxies

14:30 – 15:00 Nicolas Peschken Cosmic Ray driven winds in galaxies from MHD+Nbody simulations

15:00 – 15:15 Gabriella Di Gennaro Evidence for efficient magnetic field amplification in distant galaxy clusters


15:45 – 16:15 Gianfranco Brunetti Particle acceleration in interacting galaxy clusters

16:15 – 16:30 Simon Candelaresi Stabilizing effect of magnetic helicity on magnetic cavities in the intergalactic medium

16:30 – 17:00 Discussion 17:00 – 17:30 Break 17:30 – Banquet

MFU7 v

PROGRAM MFU7 Friday, Feb 21, 2020

Chair : Anatoly Spitkovsky

08:30 – 09:00 Dongsu Ryu Turbulence and magnetic fields in clusters of galaxies

09:00 – 09:30 Klaus Dolag Turbulence and Magnetic Fields in Cosmological Simulations

09:30 – 09:45 Ulrich Steinwandel The galactic dynamo of the Milky Way in a resovled simulation

09:45 – 10:00 Paolo Da Vela Inter Galactic Magnetic filed constrains through the gamma ray observations of the Extreme High-Peaked BL Lac Speaker HESS 1943+213

10:00 – 10:15 Paola Dominguez Fernandez Filamentary radio emission in galaxy clusters

10:15 – 10:30 Souvik Manna Low radio frequency spatially resolved studies of nearby galaxies


11:00 – 11:30 Melanie Johnston-Hollitt Cosmic Magnetism with Next Generation Radio Telescopes 11:30 – 12:00 Discussion

12:00 – 13:30 Lunch & Beach 13:30 – 14:00 Conference Summary 14:00 – 14:10 Closing Remark

Thiem Hoang

(Shu-Ichiro Inutsuka)

ABSTRACT DAY 1 Monday, February 17,2020

MFU7 1

Gradient Technique: New Way of Magnetic Field Studies Alexandre Lazarian University of Wisconsin-Madison, USA ABSTRACT : For decades the polarization measurements were the only way to study the plane-of-sky direction of magnetic field. The situation has changed as a new powerful Gradient Technique (GT) has been introduced. The technique has three main branches that use different sources of information, namely, the Velocity Gradient Technique (VGT) that employed Doppler-shifted spectroscopic data, the Synchrotron Intensity Gradients (SIGs) that use synchrotron intensity data and Synchrotron Polarization Gradients (SPGs) that use synchrotron polarization data for tomographic studies of magnetic field distribution. The GT is based on the modern understanding of MHD turbulence and turbulent reconnection, in particular, on the fact that for this type of turbulence the direction of maximal anisotropy of velocity and magnetic field fluctuations is aligned with the ambient magnetic field and it increases as the scales of motions decrease. This property of magnetic turbulence entails the conclusion that gradients of velocity and magnetic field amplitudes are perpendicular to the local direction of the magnetic field and therefore they can trace the magnetic field similar to the way polarimetry traces them. I will demonstrate the power of the new technique with (a) the example of a survey of magnetic fields of nearby molecular clouds obtained with the VGT and provide the quantitative comparison of the VGT tracing of magnetic field with the polarimetric tracing obtained by PLANCK, (b) the 3D map of magnetic field obtained by applying the VGT to various molecular species within Vela C comparing it with the 2D polarization measurements by BLASTPOL, (c) the 3D map of magnetic field in the galactic disk tested with the polarization of light coming from stars with known distances, (d) the predictions of the polarization directions and polarization intensity predicted using the VGT with the actual polarization measurements obtained with PLANCK, (e) the magnetic field for the high velocity Smith cloud for which polarization measurements are not currently feasible. I will show that the VGT can both map magnetic fields of regions of gravitational collapse as well as identify these regions. I will also compare SIGs maps with PLANCK and ATCA 1.4 GHz synchrotron polarization data and explain how the synergy of polarization and SIGs can provide detailed maps of Faraday rotation distribution. Finally, I shall demonstrate how SPGs provide detailed maps of 3D magnetic field distribution in the interstellar medium. Grain Alignment Mechanisms: Current Status and Perspectives Thiem Hoang KASI, South Korea ABSTRACT : The alignment of dust grains results in the polarization of starlight and infrared emission from themselves. Dust polarization is a popular technique to map cosmic magnetic fields and probe basic properties of dust. In this talk, I will review basic physics of grain alignment, describing the main mechanisms proposed over the last seventy years since the discovery of starlight polarization. I will demonstrate that the key requirements for efficient alignment of dust grains include grain para/super-paramagnetic susceptibility and suprathermal rotation. Grain suprathermal rotation can be induced by radiative torques arising from the interaction of irregular grains with anisotropic radiation or mechanical torques induced by gas flow. I will then show that, in intense radiation fields, grains can be spun-up to extremely fast rotation such that centrifugal force can break the grain apart. This effect is termed Radiative Torque Disruption (RATD). I will discuss the perspective of unifying RAdiative Torque (RAT) alignment and RATD and its implication for probing dust properties in various environments.

[Session 1 : Measurements and Techniques to study Magnetic Fields]


MFU7 2

Dust polarization by radiative torque alignment and disruption Hyeseung Lee Korea Astronomy and Science Institute (KASI), South Korea ABSTRACT : We model the wavelength-dependence polarization spectrum of starlight and polarized dust emission from aligned grains by radiative torques (RATs) induced by the different radiation fields. In this work, we consider a new efficient destruction mechanism by radiative torqsues, which is termed RAdiative Torque Disruption (RATD) and also RAT alignment. Using the mechanism, we find that the alignment function shifts to smaller grain sizes due to the decrease of alignment size with radiation strength (U). As a result, the peak of the starlight polarization spectrum shifts to shorter wavelengths when U increases. The rotational disruption tends to decrease the optical-near infrared polarization but increases the ultraviolet polarization due to the conversion of large grains into smaller ones, resulting in a narrower polarization curve. For polarized emission spectrum, we find that the polarization spectrum shifts to shorter wavelengths and the peak polarization tends to increase with increasing U. Our model also shows that the sub-mm polarization at 850 micron first increases with increasing U up to U ∼ 10 and then declines due to the disruption of large grains. This can qualitatively explain the observed trend reported by Planck collaboration. Based on our results, we suggest that test our theoretical model with observations of multi-wavelength polarization toward star-forming regions. Time-Varying Extinction, Polarization, and Colors of Type Ia Supernovae due to Rotational Disruption of Dust Grains Chau Giang Nguyen University of Science and Technology of Hanoi, Vietnam ABSTRACT : Photometric and polarimetric observations toward type Ia supernovae (SNe Ia) frequently report an unusually low total-to-selective extinction ratio (Rv < 2) and a small peak wavelength of polarization (lambda_max < 0.4 mu). Recently, Hoang et al. (2019) proposed that the predominance of small grains near SNe Ia due to RAdiative Torque Disruption (RATD) can explain the puzzle. To test this scenario, we perform detailed modeling of extinction and polarization of SNe Ia, accounting for grain disruption and alignment by RAdiative Torques (RATs). We find that Rv decreases from the standard value of 3.1 to ~ 1.5 after disruption time t_disr < 4 days, assuming dust clouds at distance d < 4 pc from SNe Ia. We then calculate the observed light curve of SNe Ia and find that their colors change with time due to varying dust extinction. We also find that lambda_max decreases from a standard value of ~ 0.55 mu to ~ 0.15 mu over alignment time of t_align < 10 days due to enhanced alignment of small grains. By fitting the theoretical polarization with the Serkowski law characterized by K and lambda_max parameters, we find that K tends to increase when large grains are disrupted by RATD. This feature is consistent with the unusual K vs. lambda_max relationship of SNe Ia. Finally, we discover an anti-correlation between K and Rv for dust extinction and polarization of SNe Ia. Our results demonstrate the importance of RATD on the time-dependent extinction, polarization, and colors of SNe Ia. Halo's Magnetic field as Evident from Striated Interstellar Clouds (HOMERIC) Aris Tritsis Australian National University, Australia ABSTRACT : Striations are ordered, low-column-density, quasi-periodic, elongated structures parallel to the magnetic field. The physics that drives the formation of such striations has remained a mystery since their discovery. We have performed comprehensive numerical experiments testing all possible driving mechanisms, and we have found that the only viable explanation for the appearance of striations is their formation by magnetohydrodynamic waves. The fact that striations are interstellar ripples caused by the passage of magnetosonic waves has two direct predictions: a. these waves could get trapped setting up normal modes and b. striations, being the imprint of hydromagnetic waves, can be used to measure the magnetic field.


MFU7 3

Galactic Faraday tomography at low frequencies Cameron Van Eck Dunlap Institute for Astronomy and Astrophysics, University of Toronto, Canada ABSTRACT : 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. Probing interstellar magnetic fields with radio and optical polarimetry Marijke Haverkorn Radboud University, Netherlands ABSTRACT : Both theoretical and numerical studies clearly show the multi-scale, non-gaussian, complexity of interstellar magnetic fields. Traditional observational probes of this turbulent magnetic field in the diffuse ionized medium, such as synchrotron radiation and rotation measures of extragalctic point sources, can ony give limited information since they probe average field strengths/orientations along the line of sight through the whole Milky Way. Using other tracers such as Faraday Tomography or optical interstellar polarization of stellar light, gives us the possibility to study the variations in these interstellar magnetic fields along the line of sight, opening a new dimension of study. I will attempt to review the new interstellar magnetic field studies using these techniques, and give an outlook to the SKA. Cosmic compass - First detection of an outer 3D sub-Gauss field via atomic alignment Huirong Yan DESY & , Germany University of Potsdam ABSTRACT : Sub-Gauss magnetic fields are crucial for many physical processes from Galactic kpc scale to stellar Au scale. However, all magnetic diagnoses trace only one component of a magnetic field at the best. Here we report the first observational results that unveil 3D topology as well as the strength of a sub-milliGauss magnetic field simultaneously beyond our solar system. We found that two weak neutral iron absorption lines from the ground state in the atmosphere of $89~Her$ produced counterintuitive high-amplitude polarization and consistent polarization angle, different from many other absorption lines from the excited states. This is the first observational proof in line with the theoretical prediction of the magnetic tracer ground state alignment (GSA) proposed more than a decade ago. Our analysis reveals the sub-AU scale magnetic field on 89 Her, which is 1.kpc away, has a strength 70muG ~< B ~< 150muG with a 3D orientation nearly parallel to the stellar outflow axis, thus having improved the accuracy by five digits compared to the previous 10G upper limit set by non-detection of Zeeman effect. Our observation is anticipated to usher a new era of precise measurement of sub-gauss magnetic field in the Universe.


MFU7 4

Driving Issues in Compressible MHD Turbulence Jungyeon Cho Chungnam National University (CNU) / KASI, South Korea ABSTRACT : Many astrophysical fluids are in turbulent state. To maintain turbulence, energy must be injected into the fluid. In this talk, I will discuss issues related to driving in compressible magnetohydrodynamic turbulence. First, I will briefly talk about driving scales. In turbulence simulations, it is customary to drive the fluids on a scale comparable to the size of the computational domain. However, some statistics of turbulence is changed if we do not follow the conventional approach. I will show two examples and their astrophysical implications. Second, I will talk about other factors that can effect statistics of turbulence, such as time scale and compressibility of forcing vectors. Third, I will discuss driving and turbulence in the interstellar medium. Decay of Turbulence in Fluids with Polytropic Equations of State Jeonghoon Lim Chungnam National University (CNU), South Korea ABSTRACT : In this talk, we present numerical simulations of decaying hydrodynamic turbulence initially driven by solenoidal (divergence-free) and compressive (curl-free) driving. Most previous numerical studies for decaying turbulence assume an isothermal equation of state (EOS). Here we use a polytropic EOS, P∝𝜌^𝛾 with polytropic 𝛾 ranging from 0.7 to 5/3. We mainly aim at determining the effects of polytropic 𝛾 and driving schemes on the decay law of turbulence energy, E ∝t^(-⍺). Our findings are as follows. First of all, we find that even if polytropic 𝛾 does not strongly change scaling relation of the decay law, the driving schemes weakly change the relation; in our all simulations, turbulence decays with ⍺ ≅1, but compressive driving yields smaller ⍺ than solenoidal driving at the same sonic Mach number. Second, we calculate compressive and solenoidal velocity components separately and compare their decay rates in turbulence initially driven by compressive driving. We find that the former decays much faster so that it ends up having a smaller fraction than the latter. We discuss why decay rates of compressive and solenoidal velocity components are different in compressively driven turbulence. We additionally present simulations of MHD turbulence driven by compressive driving to study its consequence on driven turbulence. Extrema of dissipation in MHD turbulence Edith Falgarone Ecole Normale Supérieure, France ABSTRACT : Turbulent dissipation is a central issue in the star and galaxy formation process, but it remains elusive in cosmic turbulence that pervades several thermal phases, is compressible, magnetized, and coupled to gravity. Turbulent dissipation is known to be intermittent in space and time. While this fundamental property has been studied theoretically and in flow experiments, it can be approached, in the case of cosmic turbulence, with a combination of observations at high spectral resolution, chemical modelling and numerical simulations. Magneto-hydrodynamical simulations dedicated to turbulent dissipation in a non-ideal fluid have shown that dissipation is concentrated in fractal structures of intense velocity shear, current and ion-neutral drift. Similar structures are now found in simulations of compressible magnetized turbulence. Most of them can be classified as shocks, current sheets or rotational discontinuities, but not all. Their observable statistical signatures in the velocity field and polarization of thermal dust emission are computed. These results will be presented and compared to recent observational data.

[Session 2 : MHD Turbulence]


MFU7 5

Cosmic compass - First detection of an outer 3D sub-Gauss field via atomic alignment Huirong Yan DESY & University of Potsdam, Germany ABSTRACT : Sub-Gauss magnetic fields are crucial for many physical processes from Galactic kpc scale to stellar Au scale. However, all magnetic diagnoses trace only one component of a magnetic field at the best. Here we report the first observational results that unveil 3D topology as well as the strength of a sub-milliGauss magnetic field simultaneously beyond our solar system. We found that two weak neutral iron absorption lines from the ground state in the atmosphere of $89~Her$ produced counterintuitive high-amplitude polarization and consistent polarization angle, different from many other absorption lines from the excited states. This is the first observational proof in line with the theoretical prediction of the magnetic tracer ground state alignment (GSA) proposed more than a decade ago. Our analysis reveals the sub-AU scale magnetic field on 89 Her, which is 1.kpc away, has a strength 70muG ~< B ~< 150muG with a 3D orientation nearly parallel to the stellar outflow axis, thus having improved the accuracy by five digits compared to the previous 10G upper limit set by non-detection of Zeeman effect. Our observation is anticipated to usher a new era of precise measurement of sub-gauss magnetic field in the Universe. Reversed dynamo, reversed helicity, and diagnosing it Axel Brandenburg NORDITA, Sweden ABSTRACT : Dynamos do work against the Lorentz force to convert kinetic energy into magnetic. But reversed dynamos do the opposite; the magnetic field does work through the Lorentz force to drive fluid motions. At large magnetic Prandtl numbers, e.g., in the interstellar medium, both happen simultaneously: a forward dynamo at large length scales and a reversed one at smaller length scales. The latter process also happens in stellar coronae. Here is also where another remarkable reversal occurs: a reversal of the magnetic helicity. A reversed helicity has been seen with in situ measurements in the solar wind, but it is also seen in models of solar and galactic dynamos. Diagnosing this through remote sensing remains a challenge. I will finish by discussing two diagnostic techniques that employ linear polarization: Faraday depolarization and the parity-odd contribution to linear polarization. Both are potentially useful to diagnosing not only astrophysical, but also laboratory plasmas. Studying Dense Structures in a Turbulent Interstellar Medium with a Moving Mesh Philip Mocz Princeton University, USA ABSTRACT : In this talk, I describe how moving mesh methods are ideal for resolving the dense structures in supersonic isothermal turbulence that ultimately form pre-stellar cores by self-gravity. Compressible turbulence establishes a network of transient dense shocks that sweep up material and have a stratified density profile described by a balance between ram pressure of the background fluid versus the magnetic and gas pressure gradient behind the shock. These rare, densest regions of a turbulent environment can become Jeans unstable and collapse to form pre-stellar cores. I present their structural properties and discuss different regimes of collapse as a function of magnetic field strength. The work provides insight into the fundamental structures of compressive turbulence and describing the initial conditions and magnetic field topology out of which protostars form.

ABSTRACT DAY 2 Tuesday, February 18,2020

MFU7 6

TBA Ethan Vishniac USA ABSTRACT : Kelvin-Helmholtz versus Tearing Instability: What Drives Turbulence in Stochastic Reconnection? Grzegorz Kowal University of Sao Paulo, Brazil ABSTRACT : Over the last few years it became clear that turbulent magnetic reconnection and magnetized turbulence are inseparable. It was not only shown that reconnection is responsible for violating the frozen-in condition in turbulence, but also that stochastic reconnection in 3D generates turbulence by itself. The actual mechanism responsible for this driving is still unknown. Processes such tearing mode or Kelvin--Helmholtz, among other plasma instabilities, could generate turbulence from irregular current sheets. We address the nature of driving mechanism for this process and consider a relative role of tearing and Kelvin--Helmholtz instabilities for the process of turbulence generation. In particular, we analyze the conditions for development of these two instabilities within three-dimensional reconnection regions. We show that both instabilities can excite turbulence fluctuations in reconnection regions. However, tearing mode has relatively slow growth rate, and at later times it becomes partially suppressed by transverse to the current sheet component of magnetic field, generated during the growth of turbulent fluctuations. On the contrary, the Kelvin--Helmholtz instability establishes quickly in the outflow region, and at later times it dominates the turbulence generation comparing to the contribution from tearing mode. Our results demonstrate that the tearing instability is subdominant compared to the the Kelvin--Helmholtz instability in terms of generation of turbulence in the 3D reconnection layers and therefore the self-driven reconnection is turbulent reconnection with tearing instability being important only at the initial stage of the reconnection. Turbulent magnetic reconnection in the kinetic regime Joerg Buechner Center for Astronomy and Astrophysics, Berlin Institute of Technology, Germany ABSTRACT : 20years ago A.Lazarian and E.T. Vishniac suggested a model of turbulent magnetic-reconnection according to which fast reconnection could be achieved in the 3D Alfvenic turbulence of high- Reynolds-number plasmas, typical for or astrophysical situations. The corresponding typical length scales were determined by the range of validity of the magnetohydrodynamic (MHD) approximation. Recently, the MMS spacecraft observed the formation of structures at plasma ion- and electron kinetic scales In the turbulent plasma of the magnetosheath of the Earths. To understand them we carried out hybrid-code (ions kinetic, electrons fluid) as well as 3D fully kinetic numerical simulations for those plasma conditions. We identified the nature of the kinetic-scale structures forming out of the turbulence, ion- and electron-scale current sheets. It appears that the kinetic scale structures allow fast magnetic reconnection at multiple sites enhancing the overall energy conversion rate similar to the case of multiple reconnection in the MHD turbulence. From the simulation results we derived observable signatures of kinetic scale turbulent magnetic reconnection.


MFU7 7

Turbulent dynamo in diverse astrophysical media Siyao Xu University of Wisconsin-Madison, USA ABSTRACT : Both turbulence and magnetic fields are ubiquitous in the Universe and exist across a vast range of length scales. The primordial magnetic fields in the early Universe were extremely weak. Turbulence is believed to account for the growth and maintenance of cosmic magnetic fields via the small-scale turbulent dynamo (SSTD), resulting in the magnetized interstellar, intracluster, and intergalactic media. Earlier theories of the SSTD were restricted to either the transient kinematic stage of dynamo or a very limited plasma parameter space. Our theories of the SSTD established from first principles are applicable to diverse astrophysical conditions with a broad range of plasma parameters and bring its applications from linear regimes to astrophysically relevant nonlinear regimes. The theoretical predictions in different physical regimes are consistent with the measurements of numerical simulations carried out by different research groups. To demonstrate its astrophysical applications, I will also discuss several examples on the dynamo amplification of magnetic fields in the weakly ionized primordial gas accompanying the first star formation, in the cosmic web accompanying the cosmic structure formation of the Universe, in a supernova remnant following the death of a star in a supernova. These dynamo-amplified magnetic fields induce fundamental astrophysical processes and have significant astrophysical implications.


MFU7 8

The JCMT BISTRO survey: submillimeter polarization spectra of thermal emission from dust grains in high-density star-forming gas Ray Furuya Institute of Liberal Arts and Sciences, Tokushima University, Japan ABSTRACT : I will present results from 450-micron linear-polarization observations of thermal emission from dust grains towards high-density star-forming molecular gas. The data were taken as the “B-fields In STar-forming Region Observations” (BISTRO) survey using the POL-2 polarimeter POL-2 in front of the Sub-millimeter Common-User Bolometer Array 2 (SCUBA-2) camera on the James Clerk Maxwell Telescope (JCMT). After briefly presenting overview of the survey, our representative B-field maps obtained from the 850 and 450-micron observations will be presented. Typical sensitivity of the POL-2 maps is almost one order of magnitude higher than the previous images, allowing us to detect weakly polarized emission, even e.g., in the periphery of molecular clouds. This enabled us to derive polarization spectra (polarization fractions across wavelengths) towards different of environments. Our analysis so far suggested that polarization spectra are likely to be shallower than previous studies, and possible reason(s) behind will be discussed. Magnetic fields and star formation in the Ophiuchus Molecular Cloud Katherine Pattle National University of Ireland Galway, England ABSTRACT : The Ophiuchus molecular cloud is one of the nearest sites of intermediate-mass star formation. The cloud, containing the active L1688 region and the more quiescent L1689 region as well as extensive filamentary streamers, is a well-known laboratory for testing star formation theories. However, despite a strong global east-to-west asymmetry in both star formation rate and interstellar radiation field (ISRF) across the cloud, star formation within the cloud also appears to vary significantly due to highly local effects. In this talk, I will present recent observations of the magnetic fields in the dense, star-forming gas of L1688 and L1689, made with the James Clerk Maxwell Telescope's (JCMT's) POL-2 polarimeter, in part by the JCMT BISTRO (B-fields in Star-forming Region Observations) survey. These observations demonstrate the highly local physics in Ophiuchus extends to the behaviour of its magnetic field, with the morphology, strength and likely effect of the magnetic field varying significantly both within and between L1688 and L1689, and from cloud to core scales within individual star-forming systems. I will discuss the implications for star formation within this heterogeneous molecular cloud. Magnetic Fields Associated with Molecular Clouds; A New Probing Technique Mehrnoosh Tahani Dominion Radio Astrophysical Observatory, National Research Council, Canada ABSTRACT : We present a new method to find the line-of-sight strength and morphology of magnetic fields in star forming regions using Faraday rotation measurements. We applied this method to four relatively nearby filamentary molecular clouds of Orion A, Orion B, Perseus, and California. In this method we use rotation measure data from the literature, a chemical evolution code, along with extinction maps of each cloud. In California and Orion A, we found clear evidence that the magnetic fields at one side of these filamentary structures are pointing towards us and are pointing away from us at the other side. We carried out further investigations to interpret our observations. The magnetic field morphologies that can explain this change of direction across these filamentary clouds include toroidal, helical, and bow morphologies. We investigated these three models by combining our results with those of Planck observations in Orion A. We found that of the three possible morphologies, toroidal is the least probable one and that the bow morphology is the most likely and natural one. Additionally, we used magnetohydrodynamics simulations to simulate filamentary molecular clouds and their magnetic field evolution. We found that helical fields are not easily generated in our tested scenarios.

[Session 3 : Magnetic Fields in Interstellar Medium]


MFU7 9

Magnetic field in S235 complex Devaraj Rangaswamy Dublin Institute for Advanced Studies, Ireland ABSTRACT : We present the magnetic (B) field properties in the S235 complex spanning a scale of ∼10pc located at a distance of 1.65 kpc. Near-infrared starlight polarimetric observations were obtained in H band using the Mimir instrument on the 1.8 m Perkins telescope, Arizona. 324 background stars were selected in the field through combination of GAIA DR2 distances and extinction from 2MASS colors. The plane-of-sky (POS) B-field directions inferred from background starlight polarimetry reveal a curved morphology tracing the spherical shell of the expanding H ii region. This indicates the B-field is frozen into the molecular gas which is compressed by the strong UV radiation from the central O9.5V star. Using Bolocam 1.1 m dust emission we extracted 9 dense molecular clumps with masses between 50 to 500 solar masses. The position of clumps correlated with high column density measured from CO data and were associated to young stellar objects. Estimation of POS B-field strength for these 9 clumps gives a mean value of ∼30 μG. The mass-to-flux ratio for all the clumps are found to be magnetically supercritical, implying that gravity dominates B-field. The mean local B-field is parallel to the large scale galactic B-field as seen from the Planck 353GHz polarized dust emission. This suggest that the molecular shell evolves preferentially along the galactic B-field direction. Our results demonstrate a weak B-field anchored along the molecular shell providing no inhibition for the occurrence of triggered star formation. On the transport and diffusion of magnetic fields in star formation Reinaldo Santos De Lima Universidade de São Paulo, Brazil ABSTRACT : Accumulation of magnetic flux during the gravitational collapse of gas in molecular clouds or during the formation of protostellar disks is a natural consequence when the magnetic field is considered ""frozen in"" to the gas in star forming environments. This could lead to situations in disagreement with observations, as the impossibility of formation of rotationally supported protostellar disks. Therefore, violation of this frozen in condition seems to be required during star formation. In the last decade turbulence has been demonstrated to produce this violation because it induces reconnection and consequently magnetic flux diffusion at a rate independent of the microphysical processes, a process termed “reconnection diffusion” (RD, Lazarian 2005). The evaluation of the role of the RD during star formation depends on the diffusivity level that it provides. One of the key parameters is the Alfvenic Mach number of the turbulence (ratio between the turbulent velocity and the Alfven velocity), and the diffusion rate is predicted by RD theory to be suppressed by a factor Ma^3 when turbulence is sub-Alfvenic (Ma < 1) and incompressible. Due to resolution limitations, it is challenging to properly represent the RD in simulations of star forming processes, and the setting of such simulations and their results interpretation depend on a firm understanding of the relation between the RD diffusion coefficient and the turbulence parameters. Aiming to test quantitatively the predictions of the RD theory in the sub-Alfvenic regime, we employed the PENCIL code to perform a series of numerical simulations of forced magneto-hydrodynamic turbulence, extracting the values of the diffusion coefficient using the Test-Field method. Our results are consistent with the RD theory in the limit of Alfvenic (incompressible) turbulence, while out of this limit the dependence of the diffusion coefficient with Ma becomes weaker. These results support and expand the RD theory predictions.


MFU7 10

Molecular Cloud Formation by Compression of Two-phase Atomic Gases Kazunari Iwasaki National Astronomical Observatory of Japan, Japan ABSTRACT : We investigate the formation of molecular clouds from atomic gas by using three-dimensional magnetohydrodynamic simulations, including non-equilibrium chemical reactions and heating/cooling processes (Iwasaki et al. 2019). We consider super-Alfvenic head-on colliding flows of atomic gas possessing the two-phase structure that consists of HI clouds and surrounding warm diffuse gas. We examine how the formation of molecular clouds depends on the angle between the upstream flow and the mean magnetic field. We find that there is a critical angle above which the shock-amplified magnetic field controls the post-shock gas dynamics. If the atomic gas is compressed almost along the mean magnetic field, super-Alfvenic anisotropic turbulence is maintained by the accretion of the highly inhomogeneous upstream atomic gas. As a result, a greatly extended turbulence-dominated post-shock layer is generated. If the angle is around the critical angle, the shock-amplified magnetic field weakens the post-shock turbulence, leading to a dense post-shock layer. For angles larger than the critical angle, the strong magnetic pressure suppresses the formation of cold dense clouds. Efficient molecular cloud formation is expected if the angle is less than a few times of the critical angle. The critical angle is found to be less than ∼15 deg. as long as the field strength is larger than 1 μG, indicating that the probability of occurrence of compression with the angles less than the critical angle is limited if shock waves come from various directions. Rotational Disruption and Desorption of Icy Grains in Protoplanetary Disks and Implications for Snowline and COMs Tung Ngo Duy University of Science and Technology of Hanoi, Vietnam ABSTRACT : Ice mantles on dust grains play an important role in various processes in protoplanetary disks, including the increase of planetesimal formation via sticking collisions of micron-sized icy grains, the formation of complex organic molecules (COMs), and reservoir of water in habitable zones. Traditionally, ice mantles are believed to be evaporated due to thermal sublimation by central stars. In this research, we will study the destruction of ice mantles using the newly discovered effects namely RAdiative Torque Disruption (RATD) by Hoang et al. (2019) and Rotation Desorption by Hoang & Tram (2019). We will show that ice mantles near the surface layer can be disrupted into small fragments. We demonstrate that the snowline is pushed downward in the presence of rotational disruption. Furthermore, we discuss the consequence of resulting fragments and find that this process can return COMs more efficient that the thermal sublimation in releasing COMs into the gas. The disruption of composite grain cores can produce nanoparticles. The reproduction of nanoparticles by RATD can explain the detection of nanodust presence throughout the disk surface and inner central region where they are supposed to be destroyed by extreme UV. Our obtained results demonstrate the significance of the disruption of dust grains and have important implications on the chemistry of protoplanetary disks.

ABSTRACT DAY 3 Wednesday, February 19,2020

MFU7 11

The role of magnetic field in the filament paradigm of star formation Shu-Ichiro Inutsuka Nagoya University, Japan ABSTRACT : Recent observations have emphasized the importance of the formation and evolution of magnetized filamentary molecular clouds in the process of star formation. Theoretical and observational investigations have provided convincing evidence for the formation of molecular cloud cores by the gravitational fragmentation of filamentary molecular clouds. The size and total angular momentum of a protoplanetary disk are supposed to be related directly to the rotational property of the parental molecular cloud core where the central protostar and surrounding disk are born. In this review we summarize our current understanding of various processes that are required in describing the filamentary molecular clouds and try to understand the origin of angular momenta of molecular cloud cores and its link to the mass function of cores and the stellar initial mass function. Impact of magnetic field on circumstellar disk formation Yusuke Tsukamoto Kagoshima University, Japan ABSTRACT : In this talk, I will talk about recent progress of theoretical studies about circumstellar disk formation. In particular, I will focus on the impact of magnetic field and non-ideal MHD effects. Recent theoretical studies have shown that non-ideal MHD effects (Ohmic diffusion, Hall effect, ambipolar diffusion) play crucial roles for protostar and circumstellar disk formation and evolution. Ohmic and ambipolar diffusion decouple the gas and the magnetic field, and significantly reduces the magnetic torque in the first core and disk, which enables the formation of the circumstellar disk at the formation epoch of protostar. Ambipolar diffusion set an upper limit to the magnetic field strength of ~ 0.1 G in and around the newly born disk (Masson+16, Tsukamoto+17). Hall effect notably changes the magnetic torques in the envelope around the disk, and strengthens or weakens the magnetic braking depending on the relative orientation of magnetic field and angular momentum (Krasnopolsky+11, Tsukamoto+15b, Tsukamoto+17). This suggests that the bimodal evolution of the disk size may realize in the early disk evolutionary phase. Hall effect and ambipolar diffusion imprint the characteristic velocity structures in the envelope of Class 0/I YSOs. Hall effect makes a counter-rotating envelope around the disk. Our simulations show that counter rotating envelope has the size of 100-1000 AU. Ambipolar diffusion causes the significant ion-neutral drift in the envelope. Our estimate show that the drift velocity of ion could become significant (~km/s ) in the Class 0/I YSOs. Magnetic Field Morphology in two Protostellar disks, a Pseudodisk, and a Protostellar jet Chin-Fei Lee Academia Sinica Institute of Astronomy and Astrophysics (ASIAA), Taiwan ABSTRACT : I will report our ALMA dust polarization observations of the disks in two protostellar systems HH 212 and HH 111 at up to 14 au resolution. The HH 212 disk is almost edge-on and could have a poloidal field, while the HH 111 disk could have both poloidal field and toroidal field. Interestingly, the HH 111 disk also has a pair of spiral arms that can be produced by gravitational instability powered by envelope accretion. I will also report our ALMA dust polarization observations of a flattened envelope around the disk in the HH 211 protostellar system. The results show that the field morphology in the flattened envelope is highly pinched and has a toroidal component, as expected if the envelope traces a pseudodisk around a rotationally supported disk. I will also report the first line polarization detection in a protostellar jet, discussing the possible field morphology in the jet.

ABSTRACT DAY 3 Wednesday, February 19,2020

MFU7 12

Highly Pinched Magnetic Fields of the Class 0 Young Stellar Object L1448 IRS 2 Woojin Kwon KASI, South Korea ABSTRACT : Magnetic fields affect star formation in a broad range of scales from parsec to hundreds au. In particular, interferometric observations and ideal magneto-hydrodynamic (MHD) simulations have reported that formation of a rotation-supported disk at the earliest young stellar objects (YSOs) is largely suppressed by magnetic fields aligned to the rotational axis of YSOs: magnetic braking. Our recent ALMA observations toward L1448 IRS 2, which has a rotation detected and its magnetic fields aligned to the rotation axis (poloidal fields) on ~1000 au scales, show that the fields switch to toroidal at the center on ~100 au scales. This result suggests that magnetic braking may not be so catastrophic for early disk formation even in YSOs with magnetic fields aligned to the rotational axis. Magnetically-controlled Gas Dynamics in Protoplanetary Disks Xuening Bai Tsinghua University, China ABSTRACT : Magnetic fields play a fundamental role in the gas dynamics in protoplanetary disks. I will briefly review theoretical and computational studies and current understandings on the gas dynamics of protoplanetary disks (PPDs), focusing on mechanisms that drive disk accretion and outflows, and global disk evolution. Thanks to improved understandings of disk microphysics, especially non-ideal magnetohydrodynamic effects, recent studies have pointed to a paradigm shift, with disk accretion and evolution primarily be driven by magnetized disk winds, which are magneto-thermal in nature with significant mass loss. This requires PPDs to be threaded by net poloidal magnetic fluxes. More fundamental question is related to the global evolution of such poloidal magnetic fluxes, which is likely connected to how disk is truncated and merges into the interstellar environment. Measuring Magnetic Fields in the Disks and Outflows of Young Stars Tom Ray Dublin Institute for Advanced Studies, Ireland ABSTRACT : Magnetic fields are considered essential to the launching of jets from young stars and to solving the "angular momentum problem" in star formation. While we know most of the basic physical parameters of jets, determining their magnetic fields has remained elusive. Here I outline the problems we face, but also show some intriguing methods we have for deriving their strength and direction. Here the next generation radio interferometers, e.g. LOFAR, are beginning to play an important role. Moreover we are starting to see unsuspected high energy phenomenon, for example, the acceleration of particles to GeV energies at parsec distances from the newborn star. Gas properties and dynamics from the cavity to the outer disk of GG Tau A Thi Phuong Nguyen Vietnam National Space Center, Vietnam ABSTRACT : I will present the analysis of CO isotopologue gas properties in the circumbinary disk and inside the cavity of a TTauri binary system, GG Tau A. A radiative transfer model, which gives density and temperature profiles of the outer ring and disk, will be presented. The temperature in the outer disk is cold and decreases steeply suggesting that stellar light being blocked by the dense inner ring. The subtraction of the best ring and disk models from the original data reveals weak emission of molecular gas inside the cavity. These observations confirm the presence of gas in dynamic evolution inside the cavity. The gas mass inside the cavity is derived amounting to a small fraction of the disk gas which departs from Keplerian motion. The estimated accretion rate is compatible stellar accretion rate.

ABSTRACT DAY 4 Thursday, February 20,2020

MFU7 13

Magnetic Reconnection Acceleration: what we have learned so far from MHD simulations with test particles Elisabete de Gouveia Dal Pino Laboratoire AstroParticule et Cosmologie (APC) - Université Paris Diderot, France ABSTRACT : Stochastic particle acceleration by magnetic reconnection still challenges theorists and observers. This process has been lately invoked to explain magnetic energy dissipation, and non-thermal emission phenomena in different astrophysical sources and environments, from stellar coronae to pulsar nebulae and black hole sources, and diffuse intergalactic and intracluster medium. In some classes of relativistic sources like blazars, this has been even claimed as the only mechanism able to explain observed extremely high energy gamma-ray flaring. Current technological limitations make it very hard, if not impossible, to detect directly magnetic reconnection or signatures of it in sources beyond the solar system. Numerical simulations have then been the most powerful tool for probing reconnection acceleration in such sources. Besides kinetic particle-in-cell (PIC) methods, magnetohydrodynamical (MHD) simulations employing test particles have been helping to shed light in the understading of this process at the macroscopic scales of these environments. In this talk I will review the most recent results of such studies and also compare them with PIC studies. Applications to black hole accretion flows and relativistic jets will be specially addressed. Gamma-ray emission from magnetised, black-hole accretion flows Juan Carlos Rodriguez-Ramirez Instituto de Astronomia, Geofísica e Ciências Atmosféricas, Universidade de São Paulo (IAG-USP), Brazil ABSTRACT : Astrophysical accelerators of cosmic-rays (CRs) can be investigated through the gamma-ray emission produced by these relativistic particles. In this talk, we discuss our results on high energy emission of relativistic particles driven by magnetic reconnection as well as by shocks occurring in the surroundings of super massive black hole (SMBH) systems. For magnetic reconnection driven particles, we simulate the propagation and emission of CRs in the surroundings of radiative-inefficient accretion flows (RIAFs) which we model with general relativistic magneto-hydrodynamics (GRMHD) together with GR radiative transfer simulations. With this approach we interpret the very-high-energy (E>100 GeV) emission associated to our galactic centre, as well as with low-luminous radio galaxies, such as Centaurus A. Using a shock particle acceleration model, we have also investigated the origin of non-thermal emission from the nuclear region of the OJ 287 blazar which, interestingly, is believed to host a SMBH binary system, thanks to a ~12 yr optical periodicity. For this source, the resulting magnetic field configuration that results from the secondary BH impact with the primary BH accretion disc, is essential to reproduce self-consistently the gamma-rays as well as the X-ray emission associated to the BH-disc flares. In this context, we are able to interpret the multi-wavelength flares observed from this putative SMBH binary source. Coherent radio emission from hot magnetic stars: What does it tell us? Barnali Das National Centre for Radio Astrophysics (NCRA)-TIFR, India ABSTRACT : I will talk about electron cyclotron maser emission (ECME) observed from a few hot magnetic stars . This type of emission has also been observed from brown dwarfs which led to the surprising discovery of the existence of kG strength magnetic field in these cool stars. Some of the characteristics of this radiation include the nearly 100% circular polarization and high directivity. With the Giant Metrewave Radio Telescope and the Very Large Array, we have observed a few of the hot magnetic stars exhibiting ECME over a wide frequency range, starting from 300 MHz to 4 GHz. These wideband observations allow us to study certain characteristics of ECME which can be used to constrain plasma density in the magnetosphere. In my talk, I will describe how we can use the emission characteristics to infer various properties of the stellar magnetosphere, and also about the rotational properties of the stars. The wideband observations also led to the discovery of a peculiar phenomenon which will also be presented here.

[Session 4 : Magnetic Fields in Compact Sources and Cosmic Acceleration]


MFU7 14

Finding pulsar magnetosphere geometry from radio polarization data Jaroslaw Dyks Copernicus Astronomical Center ABSTRACT : The orientation of pulsar magnetosphere is normally determined from the observed polarization angle curve (PA curve), which is supposed to follow the sky-projected magnetic field according to the rotating vector model (RVM). In practice, the observed PA curves usually exhibit several types of non-RVM distortions, which make the task unfeasible. With recent improvement of single pulse polarization data it becomes possible to disentangle some of these effects. The current understanding of these non-RVM effects will be described from both observational and theoretical perspective. It will be shown that complex PA distortions such as PA loops and half-orthogonal PA jumps result from superposition of radiation in two orthogonal polarization modes. The issue of whether this superposition is coherent or noncoherent will be addressed. Magnetic field generation and particle acceleration in shocks Anatoly Spitkovsky Princeton University, USA ABSTRACT : Shocks in low density plasmas (so-called "collisionless shocks") are ubiquitous throughout the Universe, and are thought to produce nonthermal particles that extend over decades in energy. I will describe the progress in modeling collisionless shock structure and particle acceleration using ab-initio kinetic simulations, focusing on the current understanding of magnetic field amplification mechanisms, the conditions necessary for particle injection into the acceleration process, and the physics behind the electron-to-ion ratio in shock acceleration. These results will be applied to understanding morphologies of shocks in supernova remnants and galaxy clusters, and to explaining the relative abundances of different species in galactic cosmic rays. Supernova Shocks in Molecular Clouds: Velocity Distribution, Combining Dynamics and Excitation of Molecular Hydrogen Ngoc Tram Le Universities Space Research Association, USA ABSTRACT : Supernovae from core collapse of massive stars drive shocks into the molecular clouds from which the stars formed. Such shocks affect future star formation from the molecular clouds, and the fast-moving, dense gas with compressed magnetic fields is associated with enhanced cosmic rays. Shock waves into dense gas are accessible to observations of molecular emission lines, including the most-abundant molecule, H2. The excitation diagram of the H2 ro-vibrational transitions is widely used as a tool to constrain the physical conditions in the molecular clouds associated with supernova remnants. However, this tool alone provides only a diagnostic for the gas column density and temperature. Using SOFIA, we observed the mid-infrared spectral line profile of the pure rotational transition H2 S(5) (J=7->5) at 6.90952 μm with the EXES spectrograph (the resolving power R=67000) toward four SNRs: IC 443 (clump B1, B2, C, and G), W28, W44 and 3C 391 in a slit of 2.4' x 9''. This extremely high-resolution spectral line, for the first time, resolved the shock velocity. We interpret this H2 S(5) spectral line using the Paris-Durham one-dimensional, plane-parallel, magneto-hydrodynamic (MHD) shock model. The a priori models are compared to the observed line profiles, showing that IC 443C, IC 443G, W44, and 3C 391 can be explained by magnetised shocks into gas with density 10^3 to 10^4 cm^-3 and strong magnetic fields. For IC 443B2, the H2 spectrum requires a J-type shock into moderate-density gas (~10^2 cm^-3) with the gas accelerated to 100 km s^-1 from its preshock location. IC 443B1 requires both a magnetic-dominated C-type shock and a J-type shock to explain the highest observed velocities. The J-type shocks that produce high-velocity molecules may be locations where the magnetic field is nearly parallel to the shock velocity, which makes it impossible for a C-type shock (with ions and neutrals separated) to form. Then, we predict the excitation diagrams from these best shock models to IC 443C, IC 443G, W44 and 3C 391 and compare them to the measurements of multiple H2 rotational lines observed by Spitzer/IRS within the same observing beams. The comparison shows the predictions match the observations perfectly for transitions with upper rotational level Jup>6, but the predictions underestimate the observations for levels with Jup<6. The extra emission from low energy levels transition poses some key problems to be addressed in the future, including whether the prominent shocked clumps were potentially star-forming cores and whether the shock waves affect their star-formation potential.


MFU7 15

Magnetic Field Amplification by Bell's Cosmic-ray Streaming Instability in Supernova Remnants Tsuyoshi Inoue Nagoya University, Japan ABSTRACT : Supernova remnants (SNRs) are believed to be the accelerator of cosmic-rays up to PeV (10^15 eV) or even more. However, in order to accelerate the cosmic-rays to PeV by the diffusive shock acceleration mechanism, magnetic field amplification is necessary. The Bell's cosmic-ray streaming instability (Bell 2004) is the most promising mechanism for the acceleration. Due to huge scale gap between the Bell instability and the SNRs, it has been very difficult to study particle acceleration under realistic conditions by numerical simulations. In this talk, using a novel method developed by Inoue (2009), we show for the first time that the Bell instability mediate cosmic-ray acceleration successfully energize cosmic-rays more than PeV at the supernova shock propagating in the dense circum stellar medium created by a stellar wind. We also discuss possibility of the spectral modulation of hadronic gamma-rays by the Bell instability from young SNRs interacting with molecular clouds. Magnetar-powered Supernovae Ke-Jung Chen Academia Sinica Institute of Astronomy and Astrophysics (ASIAA), Taiwan ABSTRACT : A newborn magnetar enclosed in a young supernova is thought to produce a luminous optical transit by tapping most of its spinning-down energy into radiation. Luminosity from the magnetar snowplows its surrounding gas and creates an expanding shell. This shell is subject to fluid instabilities and forms a big density spike that has been found in previous 1D models. Recently, multidimensional simulations suggest that the 1D density spike truncated into fragmentary structures, implying that strong fluid instabilities frequently occur inside magnetar-powered supernovae. We present a high-resolution 3D hydrodynamics simulation in 4pi geometry of a magnetar-powered supernova of a 6 Msun carbon-oxygen star. We find the shell is subject to strong fluid instabilities and that turbulent gas forms inside it. Because an extensive circumstellar medium formed before the star exploded, reverse-shock driven fluid instabilities cause additional mixing from the outer part of the ejecta. These two different mixing mechanisms together break down the spherical symmetry of the supernova ejecta. The resulting mixing of chemical elements are reflected in its spectral observation and polarized features because of the asymmetry of the ejecta. UV self-irradiated molecular shocks: probing turbulent cascades in external galaxies Andrew Lehmann Ecole Normale Superieure ABSTRACT : Observations of galactic superwinds, supernova remnants and protostellar outflows reveal a common anomaly of the detection molecules that would be destroyed by such high velocity shocks (up to ~1000 km/s). A picture has emerged of large-scale outflows triggering a turbulent cascade in a multiphase medium with significant mechanical energy dissipating in molecular shocks at much lower velocities (< 50 km/s). Modeling these shocks is key to understanding the energetics of this process and also to generate observables. We update the Paris-Durham shock model, a state-of-the-art magnetohydrodynamic shock code developed with a focus on molecular chemistry, in order to account for the UV field irradiating shocks and the self-generated UV field produced by shocks at above a critical velocity. In these moderate velocity shocks there is significant excitation of atomic hydrogen, with a large flux of Lyman alpha and beta photons escaping ahead of the shock to heat, ionize and drive molecular chemistry in a large slab of preshock gas. We discuss how Lyman alpha observations combined with tracers of the warm preshock gas and shock-heated gas constrain properties of the turbulent gas reservoirs surrounding young starburst galaxies.


MFU7 16

Probing intergalactic fields with polarisation observations Marcus Brüggen Hamburg Observatory, Germany ABSTRACT : Measuring the properties of extragalactic magnetic fields through the effect of Faraday rotation provides a means to understand the origin and evolution of cosmic magnetism. We have used data from the LOFAR Two-Metre Sky Survey (LoTSS) at 150 MHz to calculate the Faraday rotation measure (RM) of close pairs of extragalactic radio sources. By considering the RM difference between physical pairs (e.g. double-lobed radio galaxies) and non-physical pairs (i.e. close projected sources on the sky), we can statistically isolate the contribution of extragalactic magnetic fields to the total RM variance along the line of sight. This enables us to place unprecendented upper limit on the average magnetic field strength in voids and filaments that are below the Planck limits. This limit is obtained by exploring a wide range of input magnetic field strengthsin a model of cosmic over-densities that realistically reflects the observed matter inhomogeneities on large scales. Comparisons of the LOFAR RM data with a suite of cosmological MHD simulations, that explore different magnetogenesis scenarios, indicates that a strong dynamo amplification of weak primordial magnetic fields is disfavoured. Magnetisation of the large-scale structure by astrophysical processes such as galactic and AGN outflows is more consistent with the data. Cosmic Ray Acceleration in Weak Shocks in Intracluster Medium Hyesung Kang Pusan National University, South Korea ABSTRACT : From observations of radio relics, cosmic ray (CR) electrons are inferred to be accelerated via diffusive shock acceleration (DSA) in low sonic Mach number shocks induced in the intracluster medium (ICM). As in other astrophysical shocks, CR protons are expected to be accelerated at these ICM shocks, but their signatures have not been detected so far. Here we explore CR injection and acceleration via DSA in weak shocks in high beta ICM through 2D PIC simulations. We showed that the reflection of incoming particles accompanied by shock drift acceleration (SDA) is one of the key elements for particle injection to DSA, and that such processes are effective only in shocks above a critical Mach number M_c>2.3. Upstream waves excited by reflected ions and electrons govern the shock dynamics and the preacceleration process. Modeling CR electron propagation and synchrotron emission from CR-driven dynamo in spiral galaxies Michal Hanasz Institute of Astronomy, Nicolaus Copernicus University, Poland ABSTRACT : Recent theoretical and numerical studies incorporating cosmic rays (CRs) into global modeling of magnetized interstellar medium demonstrate that CRs can play an important role in generation of large-scale galactic magnetic fields and, at the same time, in driving galactic winds. Cosmic-Ray-driven dynamos produce magnetic arms in galactic disks and large-scale helical magnetic fields in galactic halos. A new element of our present model is the population of CR electrons injected in SN remnants together with CR protons. We use the recently developed Cosmic Ray Energy Spectrum (CRESP) module of PIERNIK MHD code to study propagation of CR electrons and their synchrotron emission in the magnetized interstellar medium of spiral galaxies. The CRESP module is designed for modeling energy-dependent transport, of Cosmic Ray (CR) electrons in galactic magnetic fields. The module solves the Focker-Planck equation for CR electrons characterized by a piece-wise power-law distribution function, with synchrotron and adiabatic cooling effects taken into account together with diffusive and advective propagation of CR electrons on an Eulerian grid. We use the dynamical models of spectral evolution of synchrotron emitting electrons in construction of synchrotron emission maps at different radio-frequencies together with maps of spectral index and Faraday rotation. We demonstrate that inclusion of the spectral evolution of CR electron population density opens up new opportunities for observational diagnostics of ISM dynamics and for verification of galactic dynamo models.

[Session 5 : Magnetic Fields in Compact Sources and Cosmic Acceleration]


MFU7 17

Cosmic Ray driven winds in galaxies from MHD+Nbody simulations Nicolas Peschken University Nicolaus Copernicus, Poland ABSTRACT : The magnetic field in galaxies has been shown to have direct impact on their morphology and dynamics, in particular when coupled with cosmic rays. Indeed, a growing observational evidence supports the picture of CR acceleration in supernova remnants occurring in magnetized ISM. Numerical and analytical models indicate that CRs have sufficient power to drive powerful galactic winds. This translates into large movement of gas, potentially affecting the star formation, angular momentum distribution and morphology at a galactic scale. I examine the importance of these cosmic ray driven winds and magnetic fields for galaxy evolution, by running hybrid simulations of spiral galaxies including magneto-hydrodynamics, cosmic rays as well as N-body dynamics for the stellar and dark matter components. I simulate an external inflow of gas into the galactic disc, triggering the formation of powerful winds able to leave the disc and magnetize the galactic halo. I study the formation and evolution of these winds, as well as their link with the properties of the inflow. Assuming that CRs couple dynamically with the magnetized ISM, I find that the accretion of lower angular momentum gas leads to more star formation in the disc, to stronger winds, and to consequently thicker discs, showing the impact of winds on galactic evolution, and the importance of including cosmic rays and magnetic field in galaxy simulations. Evidence for efficient magnetic field amplification in distant galaxy clusters Gabriella Di Gennaro Leiden University, Netherlands ABSTRACT : The origin and the amplification of magnetic fields during structure formation is still not understood. We report Low FrequencyArray (LOFAR) observations which reveal large-scale diffuse radio emission from galaxy clusters when the Universe was only half of its present age (i.e. z>0.6). The observed synchrotron emission indicates the existence of cosmic rays and magnetic field, associated with the dilute intracluster medium. We find that the diffuse radio emission in massive, distant clusters is common, and the high radio luminosities, in spite of the strongInverse Compton losses at high redshifts, indicates that these clusters have magnetic field strengths that are similar to those in nearby clusters. This implies that magnetic field amplification during the first phases of cluster formation is fast, which has strong implications for models of magnetogenesis Particle acceleration in interacting galaxy clusters Gianfranco Brunetti INAF- Instituto Di Radioastronomia, Italy ABSTRACT : Radio observations demonstrate the presence of non-thermal emission from the intra-cluster-medium (ICM) with different spectral properties and extending on different scales, from cluster cores to bridges connecting interacting clusters. According to the current view cluster-cluster mergers generate shocks and turbulence that ultimately dissipate part of the energy into magnetic fields and acceleration of relativistic particles. This makes a connection between the kinetic energy that is generated on large scales by cluster dynamics and the mechanisms that operate on micro-scales in the ICM. In this talk I will focus on the case of radio bridges, radio sources extending on scales of several Mpc and connecting pairs of clusters in pre-merger phase. I will propose that super-Alfvenic turbulence that is generated by the complex dynamics of substructures in filaments connecting massive clusters reaccelerates relativistic electrons via second order Fermi mechanisms producing volume filling synchrotron radiation in the form of radio bridges. I will derive expectations of non-thermal emission that will be tested with LOFAR and follow-up observations in other bands.


MFU7 18

Stabilizing effect of magnetic helicity on magnetic cavities in the intergalactic medium Simon Candelaresi University of Glasgow, Scotland ABSTRACT : We investigate the effect of magnetic helicity for the stability of buoyant magnetic cavities as found in the intergalactic medium. In these cavities we insert helical magnetic fields and test whether or not helicity can increase their stability to shredding through the Kelvin-Helmholtz instability and with that their life time. This is compared to the case of an external magnetic field which is known to reduce the growth rate of the Kelvin-Helmholtz instability. By comparing a low and high helicity configuration with the same magnetic energy we find that an internal helical magnetic field stabilizes the cavity. This effect increases as we increase the helicity content. Stabilizing the cavity with an external magnetic field requires a significantly stronger field.

ABSTRACT DAY 5 Friday, February 21,2020

MFU7 19

Turbulence and magnetic fields in clusters of galaxies Dongsu Ryu UNIST, South Korea ABSTRACT : Magnetic fields in clusters of galaxies play a critical role in shaping up the intracluster medium. Their existence has been established through the rotation measure of polarized radio galaxies and the synchrotron emission of cluster-wide diffuse sources. In the so-called Sausage relic, which is one of giant radio relics detected in a cluster outskirt, for instance, the magnetic fields are believed to have a few microG strength and a Mpc scale. The observed magnetic fields are conjectured to be produced by the process of small-scale turbulence dynamo due to turbulence in the intracluster medium (ICM). To investigate the dynamo origin, we simulate the development of turbulence and the follow-up amplification of magnetic fields in galaxy clusters using a three-dimensional MHD code. Turbulence is induced in highly stratified backgrounds expected in clusters and driven sporadically mimicking major mergers. We here present the results, aiming to answer whether the turbulence dynamo scenario can explain the observed magnetic fields in clusters of galaxies. Turbulence and Magnetic Fields in Cosmological Simulations Klaus Dolag Universitaets Sternwarte Muenchen, Germany ABSTRACT : I will give an overview of cosmological simulations of galaxies and galaxy clusters including magnetic fields, focussing especially on galaxy scale simulations to highlight our current understanding (and limits) of the magnetic field amplification in galaxies and galaxy clusters. On larger scales i will especially emphasize our current understanding of magnetic field evolution in galaxy clusters and introduce the new, 'Compass' simulation campaign for high resolution galaxy cluster simulations. The galactic dynamo of the Milky Way in a resovled simulation Ulrich Steinwandel University Observatory Munich, Germany ABSTRACT : We present a high-resolution simulation of the Milky Way with a full treatment of astrophysical MHD to resolve the small-scale and large-scale dynamo structure of the Milky Ways' galactic dynamo. Our can resolve three different stages of magnetic field growth. The initial growth phase is driven by the adiabatic collapse of gas into the dark matter potential of the galaxies. This leads to an increase of density and an amplification of the magnetic field in the limit of flux-freezing. Moreover, for the first time we show that the magnetic field amplification is supported by the small-scale turbulent dynamo which we were able to prove not only by investigating the Kazantsev-powerspectra but also the curvature of the magnetic field lines itself. Furthermore, we show the once the small-scale-turbulent dynamo saturates and strong magnetic fields are present the small-scale turbulent dynamo is ultimately switched off and the alpha-omega dynamo drives the magnetic field amplification past the equipartition regime. For the first time we investigate the Dynamo-numbers in a full galactic scale simulation and find good agreement with theoretical predictions. Finally, our simulation can reproduce observational evidence of the alpha-omega dynamo by showing a dipolar structure at early times that evolves towards a quadrupolar structure at late times. We are also able to recover radial, poloidal and vertical field reversals that are consistent with the ones observed in the Milky Way.


MFU7 20

Inter Galactic Magnetic filed constrains through the gamma ray observations of the Extreme High-Peaked BL Lac Speaker HESS 1943+213 Paolo Da Vela University of Innsbruck, Austria ABSTRACT : Extreme High Energy BL Lac (EHBL) objects are a subclass of blazars characterised by a synchrotron peak exceeding 10^17 Hz, and, in some cases, an inverse Compton peak exceeding 1 TeV. The hardness of the spectrum in the VHE band makes these sources ideal targets to study the Inter Galactic Magnetic Field (IGMF). HESS J1943+213 is a VHE (Very High Energy, E>100 GeV) γ-ray source in the direction of the Galactic Plane discovered by HESS (Abramowski et al. 2011). Recently (Archer al. 2018), VERITAS collaboration published a VHE spectrum, obtained with 31 hours of data, spanning from 200 GeV up to about 2 TeV. The two published spectra are consistent within the errors (photon index=2.8). The redshift of the source is estimated to be z<0.23. The archetypical EHBL source is 1ES 0229+200 which has a redshift z=0.14 and a similar slope in the VHE regime (photon index=2.9). Since the flux of HESS J1943+213 at 1 TeV is more than a factor of two larger than the one of 1ES 0229+200, this gives a large reprocessed power, a key element for the IGMF studies. This allowed us to study the IGMF with great accuracy. We used the simulation code CRpropa (Batista et al. 2016) to simulate the cascade emission assuming different IGMF configurations. A detailed analysis of the Fermi/LAT data, performed with the new 4FGL catalogue, gave us the opportunity to extend the observed spectrum by VERITAS and H.E.S.S. down to 1 GeV. We then compared the cascade spectrum with the combined spectra from Fermi/LAT and Cherenkov telescopes constraining the IGMF strength. Filamentary radio emission in galaxy clusters Paola Dominguez Fernandez Hamburger Sternwarte, Universität Hamburg, Germany ABSTRACT : Galaxy clusters assemble through mergers and accretion and it is through these processes that the existent magnetic fields get tangled with time. In this work, we investigate the evolution of magnetic fields in galaxy clusters. In particular, we study the origin of filamentary radio emission in the intra-cluster medium as a result of a merger event. We discuss similarities and discrepancies between results coming from cosmological MHD simulations and only MHD simulations and also the implications of our findings in the interpretation of future radio observations of galaxy clusters.


MFU7 21

Low radio frequency spatially resolved studies of nearby galaxies Souvik Manna National Centre for Radio Astrophysics (NCRA), India ABSTRACT : Magnetic fields could play important role at every scale in the star formation process from the dynamics of the galactic ISM to the fragmentation of individual star-forming cores. However, for most of the local volume galaxies of different hubble type, there is no spatially resolved map of magnetic field distribution. Therefore, we have carried out metre wavelength observations of a set of nearby galaxies with GMRT and estimated sky plane equipartition magnetic fields. We have selected a sample of 46 galaxies with angular sizes between 6' to 17' from the Local Volume Legacy (LVL) survey of galaxies within 11 Mpc (Dale etal. 2009). From our pilot observations of 7 galaxies at 325 MHz with GMRT along with their VLA archival data at 1.4 GHz, we have subtracted their thermal emissions and made spatially resolved maps of their spectral indices and magnetic fields. The magnetic fields are found to be strongest on and around their central regions and goes down by ~2-4 towards their outer parts. We have also estimated turbulent gas energy density using CO and HI data which traces molecular and atomic gas respectively. Magnetic field and turbulent gas energy densities are found to be close to their equipartition values. Magnetic field is found to vary with gas density with an average power law index of 0.46+/-0.04. We have also estimated star-formation rates using FUV and IR emission and have studied the correlation of magnetic field and star-formation rate surface density. Magnetic field is found to depend on star formation rate with a power law index of 0.30+/-0.02. Monte-Carlo simulations show that the magnetic fields for the sample galaxies vary from their equipartition values by ~25%. We are now analysing another 17 galaxies from the above sample of 46 galaxies observed with uGMRT between 300-500 MHz. With the higher sensitivity of uGMRT, we aim to study propagation of CR particles at low frequency. We also aim to see how different hubble types of galaxies effects the spatial distribution of magnetic fields with this larger sample. Cosmic Magnetism with Next Generation Radio Telescopes Melanie Johnston-Hollitt Curtin University, Australia ABSTRACT : We know that magnetic fields are pervasive across all scales in the Universe and over all of cosmic time and yet our understanding of many of the properties of magnetic fields is still limited. We do not yet know when, where or how the first magnetic fields in the Universe were formed, nor do we fully understand their role in fundamental processes such as galaxy formation or cosmic ray acceleration, or how they influence the evolution of astrophysical objects. The greatest challenge to addressing these issues has been a lack of deep, broad bandwidth polarimetric data over large areas of the sky. The Square Kilometre Array will radically improve this situation via an all-sky polarisation survey that delivers both high quality polarisation imaging in combination with observations of tens of millions of extragalactic rotation measures. Here we summarise how this survey will improve our understanding of a range of astrophysical phenomena on scales from individual Galactic objects to the cosmic web. We also discuss recent work on wide-band rotation measure synthesis and how this will improve results from next generation radio telescopes.

POSTER ABSTRACT Feb 17 – Feb 21,2020

MFU7 A

Magnetic fields in star forming regions: Protostellar jets and accretion in the outer Galaxy Thi-My-Ngan Le Institute of Astronomy, Faculty of Physics, Astronomy and Informatics, Nicolaus Copernicus University, Poland ABSTRACT : Magnetic fields are well-known to play a key role in the formation of stars (Crutcher, 2012). They influence gas accretion and launching of the jets from even low-mass protostars. Here, we investigate the properties of accretion and protostellar jets through characterizing hot and warm gas in the CMa-L224 star forming region. We use near-IR spectra obtained for 33 young stellar objects with the SpeX instrument at the NASA InfraRed Telescope Facility (IRTF). We detect HI Brɣ and H2 lines which are tracers of accretion and shocks associated with jets, respectively. We measure accretion luminosities and determine the properties of shocks in the jets, and compare them to the typical values found in more nearby star-forming regions. Numerical simulations of primary protostellar disk formation and evolution Sergey Khaibrakhmanov Ural federal University, Chelyabinsk State University, Russia ABSTRACT : We investigate the collapse of magnetic rotating protostellar clouds with mass of 1M⊙ to 10M⊙. The collapse is simulated numerically using the two-dimensional magneto-gas-dynamic code Enlil on adaptive moving mesh [1,2]. We consider the cases of weak, intermediate strength and strong magnetic field. Calculations show that magnetized rotating clouds acquire a hierarchical structure by the end of the isothermal stage of the collapse. Under the influence of electromagnetic and centrifugal forces the protostellar cloud flattens with minor to major axes ratio Z/R∼0.3-0.9 depending on the initial ratio of magnetic to gravitational energy. A geometrically and optically thin primary disk with Z/R∼0.01-0.1 forms inside the clouds. The primary disk is in quasi-magnetostatic equilibrium. The mass of primary disks is 2-20 % of the initial mass of the clouds. The primary disk contains a geometrically thin opaque disk with Z/R∼10^(-4)-10^(-3). Efficiency of the magnetic braking during the collapse is analyzed and observational appearance of primary protostellar disks is discussed. The work is supported by Russian Science Foundation (project 19-72-10012) and by Russian Foundation for Basic Research (project 18-52-52006). Dynamics of the accretion disks of young stars with large-scale magnetic field Sergey Khaibrakhmanov Ural federal University, Chelyabinsk State University, Russia ABSTRACT : We investigate the dynamics of the accretion disks of young stars with fossil large-scale magnetic field. The accretion disks of T Tauri type stars and Herbig Ae/Be stars are considered. Our model [1,2] of the accretion disks is based on the equations of magnetic gas dynamics written for the geometrically thin and optically thick disk in frame of Shakura and Sunyaev approximation. Induction equation includes Ohmic dissipation, magnetic ambipolar diffusion, magnetic buoyancy and the Hall effect. The ionization fraction is calculated considering thermal ionization, collisional ionization by cosmic rays, X-rays and radioactive decay, radiative and dissociative recombinations, recombinations onto the dust grains. Simulation show that the magnetic field geometry is quasi-azimuthal at r < 0.5-1 au. Magnetic buoyancy hinders growth of the toroidal magnetic field in this region. The magnetic field is quasi-uniform due to Ohmic dissipation inside the region of small ionization fraction (‘dead’ zone). It is quasi-radial near the borders of the ‘dead’ zone due to the Hall effect. Ambipolar diffusion hinders amplification of the radial magnetic field component outside the ‘dead’ zone, and the magnetic field geometry is quasi-azimuthal or quasi-radial depending on the ionizing radiation intensity and grain parameters. We compare our results with observations. We show that Ohmic and ambipolar heating lead to temperature growth by 100-1000 K near the borders of the ‘dead’ zone [3]. Problems of magnetic braking and outflows will also be discussed.

[Poster Session]


MFU7 B

The Stability of the Magnetic Field in Stratified stars Laura Marcela Becerra Bayona Pontificia Universidad Católica de Chile, Chile ABSTRACT : There are observations of stable magnetic field in stars of a wide range of ages, from intermediate-mass stars in the main-sequence up to degenerate stars. Despite the important role that the magnetic field plays in many astrophysical phenomena and even in the stellar evolution (i.e. accretion, mass loss, turbulence, star rotation rate, chemical composition and emission of gravitational wave), there are still many important questions regarding its origin, internal structure and the way it can survive on long timescales as the star's lifetime, namely its equilibrium and stability. The main objective of the present work is to deep in the study of the parameter space under which magnetic field configurations are stable in the stably stratified and/or barotropic interior of stars, namely characterize precisely its magnetic stable equilibrium. Then, we perform 3D-magnetohydrodynamic simulations of the evolution of magnetic field configurations in stably stratified stars with the Pencil Code. Synchrotron signatures from the cosmic-ray driven dynamo in global galactic simulations Dominik Wóltański Institute of Astronomy, Nicolaus Copernicus University, Poland ABSTRACT : We investigate synchrotron emission of galactic interstellar medium resulted from the cosmic ray driven dynamo process with the aid of a Cosmic Ray Energy Spectrum Module (CRESP) for modeling energy-dependent transport of CR electrons. The module solves the Focker-Planck equation for a piece-wise power-law distribution function, with synchrotron and adiabatic cooling effects taken into account with diffusive and advective propagation of CR electrons on an Eulerian grid. To demonstrate capabilities of the CRESP module we perform numerical simulations of the CR electron spectrum in a Milky Way-type galaxy. The simulation results allow us to construct synthetic radio-maps and spectral index maps of synchrotron radio-emission. PIERNIK MHD code: synthetic synchrotron maps of simulated edge-on galaxies possible with CRESP algorithm Mateusz Ogrodnik Institute of Astronomy | Nicolaus Copernicus University in Toruń, Poland ABSTRACT : Galactic outflows and extended non-thermal emission due to CR-electrons were observed from many edge-on galaxies, allowing i.a. to estimate the strength and vertical structure of galactic magnetic field. We apply a new algorithm of energy-dependent propagation of CR electrons in ''Cosmic Ray Energy SPectrum'' (CRESP) module of PIERNIK MHD code to model synchrotron emission of edge-on galaxies. The overall propagation of cosmic rays is described by energy-dependent diffusion-advection equation, including adiabatic cooling and synchrotron losses of CR electrons. We assume a piecewise power-law, isotropic CR distribution function and apply a conservative, finite volume-type propagation of CR gas in momentum space. We shall present models of CR-driven galactic winds for different values of CR-electron diffusion coefficient to estimate CR propagation parameters by confronting synthetic radiomaps of polarized radioemission against observational data of edge-on galaxies.


MFU7 C

Dust Rotational Dynamics in shocks: Rotational Disruption of Nanoparticles by Stochastic Mechanical Torques and Spinning Dust Emission Ngoc Tram Le Universities Space Research Association, USA ABSTRACT : Polycyclic aromatic hydrocarbons (PAHs) and nanoparticles are expected to play an important role in many astrophysical processes due to their dominant surface area, including gas heating, chemistry, star formation, and anomalous microwave emission. In dense magnetized molecular clouds where shocks are present, PAHs and nanoparticles are widely believed to originate from grain shattering due to grain–grain collisions. We present a new mechanism to destroy nanoparticles in shocks based on centrifugal stress within rapidly spinning nanoparticles spun up by stochastic atomic bombardment, which is termed rotational disruption. We find that nanoparticles can be spun up to suprathermal/thermally rotation in shock, which can make centrifugal stress exceed the maximum tensile strength of grain material, resulting in rapid disruption of nanoparticles. The proposed disruption mechanism is shown to be more efficient than thermal sputtering in controlling the lower cutoff of grain size distribution in shocks. We model microwave emission from spinning nanoparticles in shocks subject to rotational disruption. We find that rotating nanoparticles can emit strong microwave radiation, and both peak flux and peak frequency increase with increasing shock velocity. We suggest spinning dust as a new method to constrain nanoparticles and trace shock velocities in shocked dense regions. Finally, we discuss a new way that can release molecules from the nanoparticle surface into the gas in the shocked regions, which we name rotational desorption. Probing magnetic field in high-redshift galaxies using rotation measure of quasars Sunil Malik Department of Physics and Astrophysics, University of Delhi, India ABSTRACT : I will present our recent work on probing the magnetic fields of the high-redshift galaxies using the residual rotation measure of extragalactic sources. To carry out this analysis, we have compiled a large sample of 1132 quasars for which we have residual rotation measure (rrm) data as well as optical spectra to check the presence/absence of the intervening Mg II absorbers. In this analysis, we have computed broadening in the distribution of RRM using median absolute deviation from the mean (σ^md_rrm ), and found it to be 17.1∓0.7 rad m−2 for 352 sightlines having Mg II intervening absorbers in comparison to its value of 15.1∓0.6 rad m−2 for the remaining 780 sightlines without such absorbers, resulting in an excess broadening (σêx_rrm) of 17.1∓0.7 rad m−2 (significant at ~4𝞂 level) among these two subsamples. This value of (σêx_rrm) , has allowed us to constrain the average rest frame strength of the magnetic field in high redshift galaxies responsible for these Mg II absorbers, to be around ~1.3∓0.3 𝜇G at a median redshift of 0.92. This estimate of magnetic field is found to be consistent with the reported estimate in earlier studies based on Radio-IR correlation and energy equipartition for galaxies in the local universe. A similar analysis on subsample split based on the radio spectral index, α, (with F ∝ ν^α) for flat (α ≥ -0.3; 315 sightlines) and steep (α ≤ -0.7; 476 sightlines) spectrum sources shows a significant σêx_rrm (at 3.5 𝞂 level) for the former and absent in the latter. An anti-correlation is found between the σ^md_rrm and percentage polarisation (p) with almost similar Pearson correlation of -0.62 and -0.87 for subsample with and without Mg II, respectively. This suggests that the main contribution for decrements in the p value is intrinsic to the local environment of the quasars.


MFU7 D

On the relative orientation between filaments, clumps and magnetic fields Dana Alina Nazarbayev University, Kazakhstan ABSTRACT : One of the key questions about the early stages of star formation process is the role of the magnetic fields and the balance between magnetic, turbulent and gravitational energies. Evaluation of the degree of alignment between the orientations of magnetic field lines and matter structures is one of observational tools that allows us to quantitatively characterize the processes in such regions. For this, polarimetric observations provide data to derive the plane-of-the-sky magnetic field orientation. The Planck data at 353 GHz furnishes the largest amount of polarimetric measurement in the Galaxy associated with the cold dust emission. I will present a statistical analysis of the relative orientation between the magnetic fields, filaments and embedded clumps that provides a glimpse on the tendencies observed in the Milky Way in the coldest regions. We extracted 90 all over the sky using the Rolling Hough Transform – a pattern detection algorithm. We inferred magnetic field orientations within filaments using optically thin medium assumption. We compared the orientation of the hosting filaments and embedded clumps with respect to both the background and inner magnetic field, and also compared the background and inner magnetic fields orientations. We find different behaviours in terms of relative orientation depending on the environment density, and on the density contrast between the filaments and their environment. We also reveal differences in the alignment of the clumps with respect to the filaments’ magnetic field depending on the column density contrast of the hosting filaments: in particular, a bimodal distribution of the relative orientations in highly contrasted filaments. I will also present a detailed analysis of a particular case, the G202.3+2.5 filament in the Mon OB1 region in which the dynamical processes have been studied and discuss how does it fit into the common paradigm. Radio diagnostics of magnetic fields in the inner and outer corona Salvatore Mancuso INAF - Osservatorio Astrofisico di Torino, Turin, Italy ABSTRACT : We discuss the radio diagnostics of magnetic fields in the inner and outer corona as obtained through two different techniques: Faraday rotation of the polarized emission from occulted extragalactic radio sources and ground- and space-based type II burst radio spectrograph observations. We show that these two complementary techniques allow obtaining a unique estimate of the radial profile of the coronal magnetic field from about 1.1 up to 15 solar radii. We also discuss how the results from these two radio diagnostics will be further improved thanks to the enhanced capability that will be available in the very near future due to the availability of the Square Kilometre Array (SKA).


MFU7 E

Evolution and Signatures of Primordial Magnetic Fields Salome Mtchedlidze Ilia State University and Goettingen University, Georgia ABSTRACT : Different astrophysical observations (such as Faraday rotation and synchrotron emission data) performed over the last decades revealed the existence of the large-scale correlated magnetic fields with the strength of order of microGauss on galaxies and galaxy cluster scales. The origin of these extragalactic magnetic fields still remains unknown: it is commonly assumed that these fields are the result of amplification of initial weak seed fields either astrophysical or cosmological origins. The recent observations of blazar spectra suggest the lower bounds order of the femtoGauss for the magnetic fields in cosmic voids (at 1Mpc or higher length scales), and are in favor of the cosmological magnetogenesis possibility. The generation mechanisms of primordial magnetic seed fields are divided into broad classes, including inflationary and phase transition magnetogenesis scenarios. We study the magnetic fields of different primordial origins, follow the evolution of these seed fields till the late times of the Universe expansion and determine their dynamics during the large scale structure formation. To simulate the cosmic structure formation, we use the cosmological ENZO code. This allows us to examine the evolution of magnetic field and investigate its statistical properties at different cosmological environments, such as cosmic voids, filaments, and galaxy clusters. We use different initial conditions (in correspondence with various magnetogenesis scenarios), which are obtained through numerical magnetohydrodynamical simulations (using the PENCIL code) of primordial magnetic field evolution from the moment of the generation till the recombination epoch. We investigate observational signatures of outcome magnetic fields and give a prescription how to distinguish between the magnetic field primordial generation scenarios. Impact of magnetic field on the gas mass fraction of galaxy clusters Sandhya Jagannathan Ilia State University and Goettingen University, Georgia ABSTRACT : Magnetic field has been observed in both relaxed as well as unrelaxed galaxy clusters with the former possessing more strength compared to the latter. The non-thermal pressure exerted by magnetic fields contributes to the total pressure in galaxy clusters and in turn affects the estimates of the gas mass fraction, fgas. In this paper, we have considered a magnetic field strength of 10micro G for 22 unrelaxed clusters and a field strength of 10micro G as well as 20micro G for 13 relaxed clusters. The role of magnetic field has been taken into account in inferring the gas density distribution through the modication of the hydrostatic equilibrium condition (HSE). We have found that the resultant gas mass fraction is smaller with magnetic field as compared to that without magnetic field. However, this decrease is dependent on the strength and the profile of the magnetic field. We have also determined the total mass using the NFW profile to check for the dependency of fgas estimates on total mass estimators. Further, we have noted that the fgas estimates from NFW are closer to that derived from WMAP results as compared to those from HSE. From our analysis, we conclude that the non-thermal pressure from magnetic fields has a non-zero impact (of upto 4 %) on the gas mass fraction of galaxy clusters. This can further affect the measurements of angular diameter distances, cosmological parameters, and the fine structure constant.

COMMITTEE MEMBERS

MFU7 F

Elisabete de Gouveia Dal Pino (Universidade de Sao Paulo, Brasil) Edith Falgarone (Ecole Normale Superieure, Paris, France) Thiem Hoang (Korea Astronomy and Space Science Institute) Shu-Ichiro Inutsuka (Nagoya University, Japan) Alex Lazarian (University of Wisconsin-Madison, USA) Christopher McKee (University of California, Berkeley, USA) Ralph Pudritz (McMaster University, Canada) Dongsu Ryu (Ulsan Institute of Science and Technology, Korea) Tran Thanh Van (Recontres du Vietnam) Nguyen Thi Minh Phuong (Quy Nhon University) Tran Thanh Son (ICISE) Ngoc Tram Le (NASA Ames, USA & University of Science and Technology, Hanoi, Vietnam)

Science Organizing Committee

Local Organizing Committee

Scientific Organization Committee (SOC) · Tran Thanh Van (Rencontres du Vietnam) Nguyen Thi Minh...

Documents

Transcript of Scientific Organization Committee (SOC) · Tran Thanh Van (Rencontres du Vietnam) Nguyen Thi Minh...