The IMAGINE Consortium aims to bring modeling of the magnetic field of the Milky Way to a next level, by using Bayesian inference. IMAGINE includes an open-source modular software pipeline that optimizes parameters in a user-defined Galactic magnetic field model against various selected observational datasets. Bayesian priors can be added as external probabilistic constraints of the model parameters. These conference proceedings describe the science goals of the IMAGINE Consortium, the software pipeline and its inputs, viz observational data sets, Galactic magnetic field models, and Bayesian priors.
Context. The Galactic magnetic field (GMF) has a huge impact on the evolution of the Milky Way. Yet currently there exists no standard model for it, as its structure is not fully understood. In the past many parametric GMF models of varying complexity have been developed that all have been fitted to an individual set of observational data complicating comparability. Aims. Our goal is to systematize parameter inference of GMF models. We want to enable a statistical comparison of different models in the future, allow for simple refitting with respect to newly available data sets and thereby incr…
In this white paper we introduce the IMAGINE Consortium and its scientific background, goals and structure. Our purpose is to coordinate and facilitate the efforts of a diverse group of researchers in the broad areas of the interstellar medium, Galactic magnetic fields and cosmic rays, and our goal is to develop more comprehensive insights into the structures and roles of interstellar magnetic fields and their interactions with cosmic rays. To achieve a higher level of self-consistency, depth and rigour can only be achieved by the coordinated efforts of experts in diverse areas of astrophysics…
The detection of primordial B-mode polarization is still challenging due to the relatively low amplitude compared to the galactic foregrounds. To remove the contribution from the foreground, a comprehensive picture of the galactic magnetic field is indispensable. The Velocity Gradient Technique (VGT) is promising in tracing magnetic fields based on the modern understanding of the magneto-hydrodynamic turbulence. In this work, we apply VGT to a HI region containing an intermediate velocity cloud and a local velocity cloud, which are distinguishable in position-position-velocity space. We show t…
We analyse the radial and tangential velocity fields in the Galaxy as seen from the Sun by using as a first approximation a simple axisymmetric model, which we then compare with the corresponding fields in a barred N-body model of the Milky Way. This provides a global description of these quantities missing in the literature, showing where they take large values susceptible to be used in future observations even for sources well beyond the Galactic center. Absolute largest proper motions occur at a distance slightly behind the Galactic Center, which are there 1.5 times larger than the highest …
Interstellar magnetic fields play critical roles in many astrophysical processes. Yet despite their importance, our knowledge about magnetic fields in our Galaxy remains limited. For the field within the Milky Way, much of what we do know comes from observations of polarisation and Faraday rotation measures (RMs) of extragalactic sources and pulsars. A high angular density of RM measurements in several critical areas of the Galaxy is needed to clarify the Galactic magnetic field structure. Using observations made with the VLA, we have determined RMs for sources in regions of the Galactic plane…
We estimate distances to the spherical planetary nebula Abell 39 and the bipolar planetary nebula NGC 7027 by interpolating from a wide grid of photoionization models using the 3-D code, MOCASSIN. We find preliminary distances of 1.5 kpc and 0.9 kpc respectively, with uncertainties of about 30%.
We have determined 194 Faraday rotation measures (RMs) of polarized extragalactic radio sources using new, multi-channel polarization observations at frequencies around 1.4 GHz from the Very Large Array (VLA) in the Galactic plane at $17^\circ \leq l \leq 63^\circ$ and $205^\circ \leq l \leq 253^\circ$. This catalog fills in gaps in the RM coverage of the Galactic plane between the Canadian Galactic Plane Survey and Southern Galactic Plane Survey. Using this catalog we have tested the validity of recently-proposed axisymmetric and bisymmetric models of the large-scale (or regular) Galactic mag…
We model the ~1--19$\mum$ infrared (IR) extinction curve toward the Galactic Center (GC) in terms of the standard silicate-graphite interstellar dust model. The grains are taken to have a power law size distribution with an exponential decay above some size. The best-fit model for the GC IR extinction constrains the visual extinction to be Av~38--42 mag. The limitation of the model, i.e., its difficulty in simultaneously reproducing both the steep ~1--3$\mum$ near-IR extinction and the flat ~3--8$\mum$ mid-IR extinction is discussed. We argue that this difficulty could be alleviated by attribu…
The primary source of systematic uncertainty in the quest for the B-mode polarization of the Cosmic Microwave Background (CMB) introduced by primordial gravitational waves is polarized thermal emission from Galactic dust. Therefore, accurate characterization and separation of the polarized thermal dust emission is an essential step in distinguishing such a faint CMB B-mode signal. We provide a modelling framework to simulate polarized thermal dust emission based on the model described in Ghosh et al. (2017), making use of both the Planck dust and Effelsberg-Bonn HI surveys over the northern Ga…
Turbulence is a prevalent phenomenon in the interstellar medium, and in particular, the environment at the centers of galaxies. For example, detailed observations of the Milky Way's Central Molecular Zone (CMZ) revealed that it has a complex and turbulent structure. Turbulence on galactic scales is often modeled using star formation and feedback. However, these effects do not appear to be sufficient for explaining the high-velocity dispersion observed in the CMZ, indicating that additional gas-stirring processes are likely to be operating. Here we introduce a proof-of-concept method to drive t…
The stellar yields for galactic modeling applications (SYGMA) code is an open-source module that models the chemical ejecta and feedback of simple stellar populations (SSPs). It is intended for use in hydrodynamical simulations and semi-analytic models of galactic chemical evolution. The module includes the enrichment from asymptotic giant branch (AGB) stars, massive stars, SNIa and neutron-star mergers. An extensive and extendable stellar yields library includes the NuGrid yields with all elements and many isotopes up to Bi. Stellar feedback from mechanic and frequency-dependent radiative lum…
Star formation is self-regulated by its feedback that drives turbulence and heats the gas. In equilibrium, the star formation rate (SFR) should be directly related to the total (thermal plus turbulent) midplane pressure and hence the total weight of the diffuse gas if energy balance and vertical dynamical equilibrium hold simultaneously. To investigate this quantitatively, we utilize numerical hydrodynamic simulations focused on outer-disk regions where diffuse atomic gas dominates. By analyzing gas properties at saturation, we obtain relationships between the turbulence driving and dissipatio…
We use the OMEGA galactic chemical evolution code to investigate how the assumptions used for the treatment of galactic inflows and outflows impact numerical predictions. The goal is to determine how our capacity to reproduce the chemical evolution trends of a galaxy is affected by the choice of implementation used to include those physical processes. In pursuit of this goal, we experiment with three different prescriptions for galactic inflows and outflows and use OMEGA within a Markov Chain Monte Carlo code to recover the set of input parameters that best reproduces the chemical evolution of…
We discuss the global modeling of the properties of the Galactic Magnetic Field (GMF). Several improvements and variations of the model of the GMF from Jansson & Farrar (2012) (JF12) are investigated in an analysis constrained by all-sky rotation measures of extragalactic sources and polarized and unpolarized synchrotron emission data from WMAP and Planck. We present the impact of the investigated model variations on the propagation of ultrahigh-energy cosmic rays in the Galaxy.
The Sun is embedded in the so-called Local Bubble (LB) -- a cavity of hot plasma created by supernova explosions and surrounded by a shell of cold, dusty gas. Knowing the local distortion of the Galactic magnetic field associated with the LB is critical for the modeling of interstellar polarization data at high Galactic latitudes. In this his paper, we relate the structure of the Galactic magnetic field on the LB scale to three-dimensional (3D) maps of the local interstellar medium (ISM). First, we extracted the geometry of the LB shell, its inner surface, in particular from 3D dust extinction…
Modeling Emission-Line Surface Brightness in a Multiphase Galactic Wind: An O VI Case Study
University of California at Santa Barbara（加州大学圣塔芭芭拉分校）；San Diego State University（圣地亚哥州立大学）；Johns Hopkins University（约翰斯·霍普金斯大学）；Arizona State University（亚利桑那州立大学）；Stockholm University（斯德哥尔摩大学）；University of Washington（华盛顿大学）；Tel Aviv University（特拉维夫大学）
Inferences about the spatial density or phase-space structure of stellar populations in the Milky Way require a precise determination of the effective survey volume. The volume observed by surveys such as Gaia or near-infrared spectroscopic surveys, which have good coverage of the Galactic mid-plane region, is highly complex because of the abundant small-scale structure in the three-dimensional interstellar dust extinction. We introduce a novel framework for analyzing the importance of small-scale structure in the extinction. This formalism demonstrates that the spatially-complex effect of ext…
We study evolution of galactic bars using suite of very high-resolution zoom-in cosmological simulations of galaxies at z ~ 9-2. Our models were chosen to lie within similar mass DM halos, log(Mvir/Mo) ~ 11.65 +- 0.05, at z=6, 4, and 2, in high and low overdensity environments. We apply two galactic wind feedback mechanisms for each model. All galaxies develop sub-kpc stellar bars differing in their properties. We find that (1) The high-z bars form in response to various perturbations: mergers, close flybys, cold accretion inflows along the cosmological filaments, etc.; (2) These bars account …
A combination of observation, theory, modeling, and laboratory plasma experiments provides a multifaceted approach to develop a much greater understanding of how magnetic fields arise in galactic settings and how these magnetic fields mediate important processes that affect the dynamics, distribution, and composition of galactic plasmas. An important emphasis below is the opportunity to connect laboratory experiments to astrophysics. This approach is especially compelling for the galactic neighborhood, where the distribution and character of magnetic fields can be observed with greater detail …
Modeling the Milky Way wind: Supernova-driven outflows accelerate HI clouds near the Galactic center
Università di Firenze（佛罗伦萨大学）；INAF - Osservatorio Astrofisico di Arcetri（意大利国家天体物理研究所阿切特里天文台）；Research School of Astronomy and Astrophysics, The Australian National University（澳大利亚国立大学天文学与天体物理学研究学院）
Dynamical Modeling of the Broad-Line Region with High-Mass Active Galactic Nuclei and Constraints on the Virial Factor
Seoul National University（首尔大学）；California Polytechnic State University（加州州立理工大学）；University of California, Los Angeles（加州大学洛杉矶分校）；University of Michigan（密歇根大学）
Modern hydrodynamic simulations of galaxy formation are able to predict accurately the rates and locations of the assembly of giant molecular clouds in early galaxies. These clouds could host star clusters with the masses and sizes of real globular clusters. I describe current state-of-the-art simulations aimed at understanding the origin of the cluster mass function and metallicity distribution. Metallicity bimodality of globular cluster systems appears to be a natural outcome of hierarchical formation and gradually declining fraction of cold gas in galaxies. Globular cluster formation was mo…
We present KETJU, a new extension of the widely-used smoothed particle hydrodynamics simulation code GADGET-3. The key feature of the code is the inclusion of algorithmically regularized regions around every supermassive black hole (SMBH). This allows for simultaneously following global galactic-scale dynamical and astrophysical processes, while solving the dynamics of SMBHs, SMBH binaries and surrounding stellar systems at sub-parsec scales. The KETJU code includes Post-Newtonian terms in the equations of motions of the SMBHs which enables a new SMBH merger criterion based on the gravitationa…
We present inferences on the geometry and kinematics of the broad-Hbeta line-emitting region in four active galactic nuclei monitored as a part of the fall 2010 reverberation mapping campaign at MDM Observatory led by the Ohio State University. From modeling the continuum variability and response in emission-line profile changes as a function of time, we infer the geometry of the Hbeta- emitting broad line regions to be thick disks that are close to face-on to the observer with kinematics that are well-described by either elliptical orbits or inflowing gas. We measure the black hole mass to be…
Kinematically Coherent Multiphase Galactic Winds in Star-Forming Galaxies Revealed by Unified Radiative Transfer Modeling of UV Emission and Absorption Lines
Johns Hopkins University（约翰斯·霍普金斯大学）；Max-Planck Institute for Astrophysics（马克斯·普朗克天体物理学研究所）；Universität Heidelberg（海德堡大学）；Northwestern University（西北大学）；Space Telescope Science Institute（太空望远镜科学研究所）；University of Pittsburgh（匹兹堡大学）
Existing ubiquitously in the Universe with the highest luminosity, the Lyman-$α$ emission line encodes abundant physical information about the gaseous medium it interacts with. Nevertheless, the resonant nature of Ly$α$ complicates the radiative transfer (RT) modeling of the line profile, making the extraction of physical properties of the surrounding gaseous medium notoriously difficult. In this paper, we revisit the problem of deciphering the Ly$α$ emission line with RT modeling. We reveal intrinsic parameter degeneracies in the widely-used shell model in the optically thick regime for both …
This is a review of the status of efforts to model the large-scale Galactic magnetic field (GMF). Though important for a variety of astrophysical processes, the GMF remains poorly understood despite some interesting new tracers being used in the field. Though we still have too many models that might fit the data, this is not to say that the field has not developed in the last few years. In particular, surveys of polarized dust have given us a new observable that is complementary to the more traditional radio tracers, and a variety of other new tracers and related measurements are becoming avai…
This paper is an initial stage of consideration of the general problem of joint modeling of the vertical structure of a Galactic flat subsystem and the average surface of the disk of the Galaxy, taking into account the natural and measurement dispersions. We approximate the average surface of the Galactic disk with a polynomial model and determine its parameters by minimizing the squared deviations of objects along the normal to the model surface. The developed method allows us to simultaneously identify significant details of the Galactic warping and estimate the offset $z_\odot$ of the Sun r…
$Ab$ $initio$ modeling of Galactic dust polarized CMB foreground
Nanjing University（南京大学）；University of California, San Diego（加州大学圣迭戈分校）；Kavli Institute for Theoretical Physics, University of California, Santa Barbara（加州大学圣巴巴拉分校卡弗里理论物理研究所）；Los Alamos National Laboratory（洛斯阿拉莫斯国家实验室）
We investigate how the X factor, the ratio of H_2 column density (NH2) to velocity-integrated CO intensity (W), is determined by the physical properties of gas in model molecular clouds (MCs). We perform radiative transfer calculations on chemical-MHD models to compute X. Using integrated NH2 and W reproduces the limited range in X found in observations, resulting in a mean value X=2\times10^20 s/cm^2/K^1/km^1 from the Galactic MC model. However, in limited velocity intervals, X can take on a much larger range due to CO line saturation. Thus, X strongly depends on both the range in gas velocit…
The Galactic magnetic field is important in the dynamics of our Galaxy. It is believed to play a role in star formation and influence the structure of the Galaxy. In order to understand how the Galactic magnetic field originally formed or how it is evolving, we must first determine its present topology. To this end, we have used observations from the Canadian Galactic Plane Survey (CGPS) to calculate the highest source density of rotation measures (RM) to date in the disk of the Galaxy. Using these data, we estimate the Galactic longitude of the RM null point in the outer Galaxy (where the RMs…
Recent strides have been made developing dust evolution models for galaxy formation simulations but these approaches vary in their assumptions and degree of complexity. Here we introduce and compare two separate dust evolution models (labelled 'Elemental' and 'Species'), based on recent approaches, incorporated into the GIZMO code and coupled with FIRE-2 stellar feedback and ISM physics. Both models account for turbulent dust diffusion, stellar production of dust, dust growth via gas-dust accretion, and dust destruction from time-resolved supernovae, thermal sputtering in hot gas, and astratio…
We present an efficient, robust computational method for modeling the Newtonian dynamics for rotation curve analysis of thin-disk galaxies. For a disk galaxy with a typical flat rotation curve, our modeling results show that the surface mass density monotonically decreases from the galactic center toward periphery, according to Newtonian dynamics. In a large portion of the galaxy, the surface mass density follows an approximately exponential law of decay with respect to the galactic radial coordinate. Yet the radial scale length for the surface mass density seems to be generally larger than th…
In this research note, we start exploring the influence of the narrow line region (NLR) on the optical/UV continuum polarization of active galactic nuclei (AGN). We have upgraded our previous 3-component model of a thermal Seyfert nucleus that was composed of an equatorial, optically thin electron disc, a circumnuclear dusty torus, and a pair of collimated, optically thin electron winds (Marin et al.2012b). We have added a dusty extension with low optical depth to the outflows to account for continuum scattering and absorption inside the NLR. A spectropolarimetric comparison between our AGN mo…
The most widely used Galactic extinction map (Schlegel, Finkbeiner, & Davis 1998, SFD) is constructed assuming that the observed FIR fluxes entirely come from the Galactic dust. According to the earlier suggestion by Yahata et al. (2007), we consider how far-infrared (FIR) emission of galaxies affects the SFD map. We first compute the surface number density of SDSS DR7 galaxies as a function of the $r$-band extinction, $A_{r,\rm SFD}$. We confirm that the surface densities of those galaxies positively correlate with $A_{r,\rm SFD}$ for $A_{r,\rm SFD}<0.1$, as first discovered by Yahata et al. …
Comparisons between observational surveys and galaxy formation models find that the mass of dark matter haloes can largely explain galaxies' stellar mass. However, it remains uncertain whether additional environmental variables, generally referred to as assembly bias, are necessary to explain other galaxy properties. We use the Illustris Simulation to investigate the role of assembly bias in producing galactic conformity by considering 18,000 galaxies with $M_{stellar}$ > $2 \times 10^9$ $M_{\odot}$. We find a significant signal of galactic conformity: out to distances of about 10 Mpc, the mea…
We present a numerical model developed to calculate observed fluxes of relativistic jets in active galactic nuclei. The observed flux of each turbulent eddy is dependent upon its variable Doppler boosting factor, computed as a function of the relativistic sum of the individual eddy and bulk jet velocities and our viewing angle to the jet. The total observed flux is found by integrating the radiation from the eddies over the turbulent spectrum. We consider jets that contain turbulent eddies that have either standard Kolmogorov or recently derived relativistic turbulence spectra. We also account…
We present an updated version of POLARIS, a well established code designated for dust polarisation and line radiative transfer (RT) in arbitrary astrophysical environments. We extend the already available capabilities with a synchrotron feature for polarised emission. Here, we combine state-of-the-art solutions of the synchrotron RT coefficients with numerical methods for solving the complete system of equations of the RT problem, including Faraday rotation (FR) as well as Faraday conversion (FC). We validate the code against Galactic and extragalactic observations by performing a statistical …
A suite of vast stellar surveys mapping the Milky Way, culminating in the Gaia mission, is revolutionizing the empirical information about the distribution and properties of stars in the Galactic stellar disk. We review and lay out what analysis and modeling machinery needs to be in place to test mechanisms of disk galaxy evolution and to stringently constrain the Galactic gravitational potential, using such Galactic star-by-star measurements. We stress the crucial role of stellar survey selection functions in any such modeling; and we advocate the utility of viewing the Galactic stellar disk …
There is a continued debate as to the form of the outer disc of the Milky Way galaxy, which has important implications for its formation. Stars are known to exist at a galacto-centric distance of at least 20 kpc. However, there is much debate as to whether these stars can be explained as being part of the disc or whether another extra galactic structure, the so called Monoceros ring/stream, is required. To examine the outer disc of the Galaxy toward the anti-centre to determine whether the star counts can be explained by the thin and thick discs alone. Using Sloan star counts and extracting th…
We present a new extended and detailed set of models for Classical Cepheid pulsators at solar chemical composition ($Z=0.02$, $Y=0.28$) based on a well tested nonlinear hydrodynamical approach. In order to model the possible dependence on crucial assumptions such as the Mass-Luminosity relation of central Helium burning intermediate-mass stars or the efficiency of superadiabatic convection, the model set was computed by varying not only the pulsation mode and the stellar mass but also the Mass-Luminosity relation and the mixing length parameter that is used to close the system of nonlinear hyd…
An empirical forward-modeling framework is developed to interpret the multiwavelength properties of Active Galactic Nuclei (AGN) and provide insights into the overlap and incompleteness of samples selected at different parts of the electromagnetic spectrum. The core of the model are observationally derived probabilites on the occupation of galaxies by X-ray selected AGN. These are used to seed mock galaxies drawn from stellar-mass functions with accretion events and then associate them with spectral energy distributions that describe both the stellar and AGN emission components. This approach …
Cosmic ray (CR) sources leave signatures in the isotopic abundances of CRs. Current models of Galactic CRs that consider supernovae (SNe) shocks as the main sites of particle acceleration cannot satisfactorily explain the higher ${\rm ^{22}Ne/^{20}Ne}$ ratio in CRs compared to the interstellar medium. Although stellar winds from massive stars have been invoked, their contribution relative to SNe ejecta has been taken as a free parameter. Here we present a theoretical calculation of the relative contributions of wind termination shocks (WTSs) and SNe shocks in superbubbles, based on the hydrody…
It has long been recognized that magnetic fields play an important role in many astrophysical environments, yet the strength and structure of magnetic fields beyond our solar system have been at best only qualitatively constrained. The Galactic magnetic field in particular is crucial for modeling the transport of Galactic CRs, for calculating the background to dark matter and CMB-cosmology studies, and for determining the sources of UHECRs. This report gives a brief overview of recent major advances in our understanding of the Galactic magnetic field (GMF) and its lensing of Galactic and ultra…
