scholarly journals INTERPRETATION OF THE LARGE-SCALE EMISSION FROM THE GALACTIC PLANE

1981 ◽  
Vol 96 ◽  
pp. 261-274
Author(s):  
S. Drapatz
Keyword(s):  
Gamma Radiation ◽  
Interstellar Dust ◽  
Large Scale ◽  
Galactic Plane ◽  
Galactic Disk ◽  
Point Sources ◽  
Infrared Astronomy ◽  
Electromagnetic Spectrum ◽  
Interstellar Gas ◽  
To Come

To obtain information on the large-scale structure of our Galaxy, one has to investigate the radiation in the short-wavelength and long-wavelength portion of the electromagnetic spectrum where attenuation throughout the whole galactic disk is very low: gamma-radiation on the one-hand side and infrared and radio radiation on the other side. But since most of the different modes of radiation are generated by interaction of two or more basic galactic constituents one derives only indirect information on a specific component. To come as close to a unique solution as possible the results of as many different spectral regions as possible should be combined. From this point of view it is very encouraging that infrared astronomy has been entering the field and will continue to contribute in the years to come. While gamma-radiation presents mainly information about the cosmic rays and the interstellar gas and radio astronomy about early-type stars and the interstellar gas, infrared astronomy has opened a new way to investigate a major fraction of the stellar population and the interstellar dust. The information is contained in the diffuse galactic emission, which is observed at low galactic latitudes with a field of view large enough to discriminate against point sources, i.e. the emission is averaged over typical dimensions of some 100 pc.

scholarly journals Remarkable Symmetries in the Milky Way Disc's Magnetic Field

2011 ◽  
Vol 28 (2) ◽  
pp. 171-176 ◽  
Author(s):  
P. P. Kronberg ◽  
K. J. Newton-McGee
Keyword(s):  
Magnetic Structure ◽  
Large Scale ◽  
Milky Way ◽  
Galactic Center ◽  
Galactic Plane ◽  
Galactic Disk ◽  
Field Structure ◽  
Field Pattern ◽  
Close Coupling ◽  
Sign Change

AbstractWe apply a new, expanded compilation of extragalactic source Faraday rotation measures (RM) to investigate the broad underlying magnetic structure of the Galactic disk at latitudes ∣b∣ ≲15° over all longitudes l, where our total number of RMs is comparable to those in the combined Canadian Galactic Plane Survey (CGPS) at ∣b∣ < 4° and the Southern Galactic Plane (SGPS) ∣b∣<1.5°. We report newly revealed, remarkably coherent patterns of RM at ∣b∣≲15° from l∼270° to ∼90° and RM(l) features of unprecedented clarity that replicate in l with opposite sign on opposite sides of the Galactic center. They confirm a highly patterned bisymmetric field structure toward the inner disc, an axisymmetic pattern toward the outer disc, and a very close coupling between the CGPS/SGPS RMs at ∣b∣≲3° (‘mid-plane’) and our new RMs up to ∣b∣∼15° (‘near-plane’). Our analysis also shows the vertical height of the coherent component of the disc field above the Galactic disc's mid-plane—to be ∼1.5 kpc out to ∼6 kpc from the Sun. This identifies the approximate height of a transition layer to the halo field structure. We find no RM sign change across the plane within ∣b∣∼15° in any longitude range. The prevailing disc field pattern and its striking degree of large-scale ordering confirm that our side of the Milky Way has a very organized underlying magnetic structure, for which the inward spiral pitch angle is 5.5°±1° at all ∣b∣ up to ∼12° in the inner semicircle of Galactic longitudes. It decreases to ∼0° toward the anticentre.

scholarly journals The magnetic structure of our Galaxy: a review of observations

2008 ◽  
Vol 4 (S259) ◽  
pp. 455-466 ◽  
Author(s):  
JinLin Han
Keyword(s):  
Magnetic Fields ◽  
Magnetic Structure ◽  
Large Scale ◽  
Galactic Halo ◽  
Galactic Center ◽  
Galactic Plane ◽  
Galactic Disk ◽  
Dust Emission ◽  
Measure Data ◽  
Radio Sources

AbstractThe magnetic structure in the Galactic disk, the Galactic center and the Galactic halo can be delineated more clearly than ever before. In the Galactic disk, the magnetic structure has been revealed by starlight polarization within 2 or 3 kpc of the Solar vicinity, by the distribution of the Zeeman splitting of OH masers in two or three nearby spiral arms, and by pulsar dispersion measures and rotation measures in nearly half of the disk. The polarized thermal dust emission of clouds at infrared, mm and submm wavelengths and the diffuse synchrotron emission are also related to the large-scale magnetic field in the disk. The rotation measures of extragalactic radio sources at low Galactic latitudes can be modeled by electron distributions and large-scale magnetic fields. The statistical properties of the magnetized interstellar medium at various scales have been studied using rotation measure data and polarization data. In the Galactic center, the non-thermal filaments indicate poloidal fields. There is no consensus on the field strength, maybe mG, maybe tens of μG. The polarized dust emission and much enhanced rotation measures of background radio sources are probably related to toroidal fields. In the Galactic halo, the antisymmetric RM sky reveals large-scale toroidal fields with reversed directions above and below the Galactic plane. Magnetic fields from all parts of our Galaxy are connected to form a global field structure. More observations are needed to explore the untouched regions and delineate how fields in different parts are connected.

Evidence for Large Scale Cosmic Ray Electron Gradients in the Galaxy

1976 ◽  
Vol 3 (1) ◽  
pp. 1-6 ◽  
Author(s):  
W. R. Webber
Keyword(s):  
Large Scale ◽  
Spiral Structure ◽  
Cosmic Ray ◽  
Point Sources ◽  
Interstellar Matter ◽  
Interstellar Gas ◽  
The Galaxy ◽  
Ray Density ◽  
Γ Rays ◽  
Γ Ray

In recent years observations of γ-ray emission from the disk of the galaxy have provided a new opportunity for research into the structure of the spiral arms of our own galaxy. In Figure 1 we show a map of the structure of the disk of the galaxy as observed for γ-rays of energy > 100 MeV by the SAS-2 satellite (Fichtel et al. 1975). The angular resolution of these measurements is ~ 3°, and besides two point sources at l = 190° and 265° several features related to the spiral structure of the galaxy are evident in the data. Most of these γ-rays are believed to arise from the decay of π° mesons produced by the nuclear interactions of cosmic rays (mostly protons) with the ambient interstellar gas. As a result, the γ-ray fluxes represent a measure of the line of sight integral of the product of the cosmic ray density NCR and the interstellar matter density N1

scholarly journals Three-dimensional maps of interstellar dust in the Local Arm: using Gaia, 2MASS, and APOGEE-DR14

2018 ◽  
Vol 616 ◽  
pp. A132 ◽  
Author(s):  
R. Lallement ◽  
L. Capitanio ◽  
L. Ruiz-Dern ◽  
C. Danielski ◽  
C. Babusiaux ◽  
...  
Keyword(s):  
Interstellar Dust ◽  
Large Scale ◽  
Galactic Plane ◽  
Large Fraction ◽  
Complex Structure ◽  
Dust Emission ◽  
Three Dimensional ◽  
Red Giants ◽  
Photometric Calibration ◽  
The One

Context. Gaia data and stellar surveys open the way to the construction of detailed 3D maps of the Galactic interstellar (IS) dust based on the synthesis of star distances and extinctions. Dust maps are tools of broad use, also for Gaia-related Milky Way studies. Aims. Reliable extinction measurements require very accurate photometric calibrations. We show the first step of an iterative process linking 3D dust maps and photometric calibrations, and improving them simultaneously. Methods. Our previous 3D map of nearby IS dust was used to select low-reddening SDSS/APOGEE-DR14 red giants, and this database served for an empirical effective temperature- and metallicity-dependent photometric calibration in the Gaia G and 2MASS Ks bands. This calibration has been combined with Gaia G-band empirical extinction coefficients recently published, G, J, and Ks photometry and APOGEE atmospheric parameters to derive the extinction of a large fraction of the survey targets. Distances were estimated independently using isochrones and the magnitude-independent extinction KJ−Ks. This new dataset has been merged with the one used for the earlier version of dust map. A new Bayesian inversion of distance-extinction pairs has been performed to produce an updated 3D map. Results. We present several properties of the new map. A comparison with 2D dust emission reveals that all large dust shells seen in emission at middle and high latitudes are closer than 300 pc. The updated distribution constrains the well-debated, X-ray bright North Polar Spur to originate beyond 800 pc. We use the Orion region to illustrate additional details and distant clouds. On the large scale the map reveals a complex structure of the Local Arm. Chains of clouds of 2–3 kpc in length appear in planes tilted by ≃15° with respect to the Galactic plane. A series of cavities oriented along a l ≃ 60–240° axis crosses the Arm. Conclusions. The results illustrate the ongoing synergy between 3D mapping of IS dust and stellar calibrations in the context of Gaia. Dust maps provide prior foregrounds for future calibrations appropriate to different target characteristics or ranges of extinction, allowing us in turn to increase extinction data and produce more detailed and extended maps.

scholarly journals A (2). Overall Structure: Space Distribution and Motions in the Disk

1955 ◽  
Vol 1 ◽  
pp. 13-24
Keyword(s):  
Large Scale ◽  
Galactic Plane ◽  
Large Scale Structure ◽  
Scale Structure ◽  
Space Distribution ◽  
Interstellar Gas ◽  
Giant Stars ◽  
Galactic System ◽  
Wide Range ◽  
The Common

The population of the disk consists of a great variety of objects with a wide range of concentration towards the galactic plane and of peculiar motions. The extreme population I objects like interstellar gas and dust and super-giant stars, show quite different properties with respect to space distribution and motions, compared to such stars as, for instance, the common G and K giants. The discussions at the conference have concentrated on the observational possibilities of studying the correlation—or the lack of correlation—between the space distributions of different kinds of objects. From recent theoretical as well as observational work it has become apparent that there is a wide range in the ages of the stars contributing to the disk population, from a few million so some 1000 million years. The differences in the distributions of the various kinds of stars very probably must be interpreted in terms of these differences in age and evolution. The most intriguing problem for the present thus seems to be this: Can we trace large-scale structure in the distribution of objects of different ages, and can we derive information on the evolution of the galactic system and of the stars themselves from the degree of resemblance in the large-scale structure exhibited by different objects?

scholarly journals Large scale magnetic fields of our Galaxy

2009 ◽  
Vol 5 (H15) ◽  
pp. 450-451
Author(s):  
JinLin Han
Keyword(s):  
Star Formation ◽  
Magnetic Fields ◽  
Large Scale ◽  
Galactic Halo ◽  
Galactic Center ◽  
Galactic Plane ◽  
Galactic Disk ◽  
Zeeman Splitting ◽  
Radio Sources ◽  
Star Formation Regions

AbstractLarge-scale magnetic fields in the Galactic disk have been revealed by distributions of pulsar rotation measures (RMs) and Zeeman splitting data of masers in star formation regions, which have several reversals in arm and interarm regions. Magnetic fields in the Galactic halo are reflected by the antisymmetric sky distribution of RMs of extragalactic radio sources, which have azimuthal structure with reversed directions below and above the Galactic plane. Large-scale magnetic fields in the Galactic center probably have a poloidal and toroidal structure.

scholarly journals Large Scale Magnetohydrodynamical Considerations in Spiral Galaxies

1983 ◽  
Vol 100 ◽  
pp. 157-158
Author(s):  
E. Battaner ◽  
M. L. Sánchez-Saavedra
Keyword(s):  
Magnetic Field ◽  
Steady State ◽  
Velocity Field ◽  
Large Scale ◽  
Spiral Galaxies ◽  
Galactic Center ◽  
Galactic Plane ◽  
Interstellar Gas ◽  
Plasma Distribution ◽  
Ring Structures

A magnetohydrodynamical result is deduced, which could contribute to our understanding of spiral and ring structures in galaxies. The usual expressions for the continuity, momentum and induction equations are adopted for the gas of a galaxy, and the following simplifying hypotesis are made : a) Steady state conditions, b) Axisymmetry, c) A velocity field given by (π=0, θ=θ(r), Z=0) for the interstellar gas (where π,θ and Z are the radial, azimuthal and vertical to the galactic plane components and r is the distance from the galactic center). Then, the direction of magnetic field must be azimuthal and the plasma distribution is compatible with ring structures.

scholarly journals Faraday Rotation of Extended Emission as a Probe of the Large-Scale Galactic Magnetic Field

Galaxies ◽  
2019 ◽  
Vol 7 (2) ◽  
pp. 43 ◽  
Author(s):  
Anna Ordog ◽  
Rebecca Booth ◽  
Cameron Van Eck ◽  
Jo-Anne Brown ◽  
Thomas Landecker
Keyword(s):  
Magnetic Field ◽  
Faraday Rotation ◽  
Large Scale ◽  
Galactic Plane ◽  
Galactic Disk ◽  
Galactic Magnetic Field ◽  
Galactocentric Distance ◽  
Linear Fit ◽  
Unused Resource ◽  
Extended Emission

The Galactic magnetic field is an integral constituent of the interstellar medium (ISM), and knowledge of its structure is crucial to understanding Galactic dynamics. The Rotation Measures (RM) of extragalactic (EG) sources have been the basis of comprehensive Galactic magnetic field models. Polarised extended emission (XE) is also seen along lines of sight through the Galactic disk, and also displays the effects of Faraday rotation. Our aim is to investigate and understand the relationship between EG and XE RMs near the Galactic plane, and to determine how the XE RMs, a hitherto unused resource, can be used as a probe of the large-scale Galactic magnetic field. We used polarisation data from the Canadian Galactic Plane Survey (CGPS), observed near 1420 MHz with the Dominion Radio Astrophysical Observatory (DRAO) Synthesis Telescope. We calculated RMs from a linear fit to the polarisation angles as a function of wavelength squared in four frequency channels, for both the EG sources and the XE. Across the CGPS area, 55 ∘ < ℓ < 193 ∘ , − 3 ∘ < b < 5 ∘ , the RMs of the XE closely track the RMs of the EG sources, with XE RMs about half the value of EG-source RMs. The exceptions are places where large local HII complexes heavily depolarise more distant emission. We conclude that there is valuable information in the XE RM dataset. The factor of 2 between the two types of RM values is close to that expected from a Burn slab model of the ISM. This result indicates that, at least in the outer Galaxy, the EG and XE sources are likely probing similar depths, and that the Faraday rotating medium and the synchrotron emitting medium have similar variation with galactocentric distance.

scholarly journals Galactic dust and extinction

1979 ◽  
Vol 84 ◽  
pp. 87-92 ◽  
Author(s):  
Gösta Lyngå
Keyword(s):  
Interstellar Dust ◽  
Large Scale ◽  
Galactic Plane ◽  
Dark Clouds ◽  
Gould Belt ◽  
Dust Clouds ◽  
Visual Extinction ◽  
Colour Excess ◽  
The Galaxy

The ratio R between visual extinction and colour excess, is slightly larger than 3 and does not vary much throughout our part of the Galaxy. The distribution of dust in the galactic plane shows, on the large scale, a gradient with higher colour excesses towards 1=50° than towards 1=230°. On the smaller scale, much of the dust responsible for extinction is situated in clouds which tend to group together. The correlation between positions of interstellar dust clouds and positions of spiral tracers seems rather poor in our Galaxy. However, concentrated dark clouds as well as extended regions of dust show an inclined distribution similar to the Gould belt of bright stars.

scholarly journals The VISTA Variables in the Vía Láctea infrared variability catalogue (VIVA-I)

2020 ◽  
Vol 496 (2) ◽  
pp. 1730-1756 ◽  
Author(s):  
C E Ferreira Lopes ◽  
N J G Cross ◽  
M Catelan ◽  
D Minniti ◽  
M Hempel ◽  
...  
Keyword(s):  
Large Scale ◽  
Near Infrared ◽  
Gamma Ray ◽  
Galactic Plane ◽  
Point Sources ◽  
The Other ◽  
Complete Sample ◽  
Good Opportunity ◽  
Variability Analysis ◽  
Near Ir

ABSTRACT High extinction and crowding create a natural limitation for optical surveys towards the central regions of the Milky Way, where the gas and dust are mainly confined. Large-scale near-infrared (IR) surveys of the Galactic plane and bulge are a good opportunity to explore open scientific questions as well as to test our capability to explore future data sets efficiently. Thanks to the VISTA Variables in the Vía Láctea (VVV) ESO public survey, it is now possible to explore a large number of objects in those regions. This paper addresses the variability analysis of all VVV point sources having more than 10 observations in VVVDR4 using a novel approach. In total, the near-IR light curves of 288 378 769 sources were analysed using methods developed in the New Insight Into Time Series Analysis project. As a result, we present a complete sample having 44 998 752 variable star candidates (VVV-CVSC), which include accurate individual coordinates, near-IR magnitudes (Z,Y,J, and Hs), extinctions A(Ks), variability indices, periods, amplitudes, among other parameters to assess the science. Unfortunately, a side effect of having a highly complete sample, is also having a high level of contamination by non-variable (contamination ratio of non-variables to variables is slightly over 10:1). To deal with this, we also provide some flags and parameters that can be used by the community to decrease the number of variable candidates without heavily decreasing the completeness of the sample. In particular, we cross-identified 339 601 of our sources with Simbad and AAVSO data bases, which provide us with information for these objects at other wavelengths. This subsample constitutes a unique resource to study the corresponding near-IR variability of known sources as well as to assess the IR variability related with X-ray and gamma-ray sources. On the other hand, the other ${\sim }99.5{{\ \rm per\ cent}}$ sources in our sample constitutes a number of potentially new objects with variability information for the heavily crowded and reddened regions of the Galactic plane and bulge. The present results also provide an important queryable resource to perform variability analysis and to characterize ongoing and future surveys like TESS and LSST.

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