scholarly journals Can we detect Galactic spiral arms? 3D dust distribution in the Milky Way

2017 ◽  
Vol 12 (S330) ◽  
pp. 189-192 ◽  
Author(s):  
Sara Rezaei Kh. ◽  
Coryn A. L. Bailer-Jones ◽  
Morgan Fouesneau ◽  
Richard Hanson
Keyword(s):  
Spatial Correlation ◽  
High Precision ◽  
Milky Way ◽  
Precision Measurements ◽  
Line Of Sight ◽  
Spiral Arms ◽  
Dust Extinction ◽  
The Galaxy ◽  
Galactic Spiral ◽  
Dust Distribution

AbstractWe present a model to map the 3D distribution of dust in the Milky Way. Although dust is just a tiny fraction of what comprises the Galaxy, it plays an important role in various processes. In recent years various maps of dust extinction have been produced, but we still lack a good knowledge of the dust distribution. Our presented approach leverages line-of-sight extinctions towards stars in the Galaxy at measured distances. Since extinction is proportional to the integral of the dust density towards a given star, it is possible to reconstruct the 3D distribution of dust by combining many lines-of-sight in a model accounting for the spatial correlation of the dust. Such a technique can be used to infer the most probable 3D distribution of dust in the Galaxy even in regions which have not been observed. This contribution provides one of the first maps which does not show the “fingers of God” effect. Furthermore, we show that expected high precision measurements of distances and extinctions offer the possibility of mapping the spiral arms in the Galaxy.

scholarly journals Synthetic 26Al emission from galactic-scale superbubble simulations

2019 ◽  
Vol 490 (2) ◽  
pp. 1894-1912 ◽  
Author(s):  
D Rodgers-Lee ◽  
M G H Krause ◽  
J Dale ◽  
R Diehl
Keyword(s):  
Milky Way ◽  
Formation Rate ◽  
Radioactive Decay ◽  
Line Of Sight ◽  
Galactic Rotation ◽  
Spiral Arms ◽  
Hydrodynamic Simulations ◽  
Doppler Shifts ◽  
Γ Ray ◽  
Halo Gas

ABSTRACT Emission from the radioactive trace element 26Al has been observed throughout the Milky Way with the COMPTEL and INTEGRAL satellites. In particular, the Doppler shifts measured with INTEGRAL connect 26Al with superbubbles, which may guide 26Al flows off spiral arms in the direction of Galactic rotation. In order to test this paradigm, we have performed galaxy-scale simulations of superbubbles with 26Al injection in a Milky Way-type galaxy. We produce all-sky synthetic γ-ray emission maps of the simulated galaxies. We find that the 1809 keV emission from the radioactive decay of 26Al is highly variable with time and the observer’s position. This allows us to estimate an additional systematic variability of 0.2 dex for a star formation rate derived from 26Al for different times and measurement locations in Milky Way-type galaxies. High-latitude morphological features indicate nearby emission with correspondingly high-integrated γ-ray intensities. We demonstrate that the 26Al scale height from our simulated galaxies depends on the assumed halo gas density. We present the first synthetic 1809 keV longitude-velocity diagrams from 3D hydrodynamic simulations. The line-of-sight velocities for 26Al can be significantly different from the line-of-sight velocities associated with the cold gas. Over time, 26Al velocities consistent with the INTEGRAL observations, within uncertainties, appear at any given longitude, broadly supporting previous suggestions that 26Al injected into expanding superbubbles by massive stars may be responsible for the high velocities found in the INTEGRAL observations. We discuss the effect of systematically varying the location of the superbubbles relative to the spiral arms.

scholarly journals Interarm islands in the Milky Way – the one near the Cygnus spiral arm

2020 ◽  
Vol 494 (1) ◽  
pp. 1134-1142
Author(s):  
Jacques P Vallée
Keyword(s):  
Observational Data ◽  
Milky Way ◽  
Young Stars ◽  
H Ii Regions ◽  
Spiral Arms ◽  
The Galaxy ◽  
The One ◽  
Loop 2 ◽  
Perseus Arm ◽  
Spiral Arm

ABSTRACT This study extends to the structure of the Galaxy. Our main goal is to focus on the first spiral arm beyond the Perseus arm, often called the Cygnus arm or the ‘Outer Norma’ arm, by appraising the distributions of the masers near the Cygnus arm. The method is to employ masers whose trigonometric distances were measured with accuracy. The maser data come from published literature – see column 8 in Table 1 here, having been obtained via the existing networks (US VLBA, the Japanese VERA, the European VLBI, and the Australian LBA). The new results for Cygnus are split in two groups: those located near a recent CO-fitted global model spiral arm and those congregating within an ‘interarm island’ located halfway between the Perseus arm and the Cygnus arm. Next, we compare this island with other similar interarm objects near other spiral arms. Thus, we delineate an interarm island (6 × 2 kpc) located between the two long spiral arms (Cygnus and Perseus arms); this is reminiscent of the small ‘Local Orion arm’ (4 × 2 kpc) found earlier between the Perseus and Sagittarius arms and of the old ‘Loop’ (2 × 0.5 kpc) found earlier between the Sagittarius and Scutum arms. Various arm models are compared, based on observational data (masers, H II regions, H I gas, young stars, CO 1–0 gas).

scholarly journals Fluctuations of the Diffuse Galactic Background

1990 ◽  
Vol 139 ◽  
pp. 99-99
Author(s):  
K. Mattila
Keyword(s):  
Milky Way ◽  
Interstellar Matter ◽  
Observational Material ◽  
The Galaxy ◽  
The Mean ◽  
Dust Distribution ◽  
Galactic Background

An analysis of fluctuations in the brightness of the Milky Way using the concept that interstellar matter occurs in the form of discrete clouds was first applied by Ambarzumian (1940, 1944). This theory was formulated in a general way and discussed in great detail in a series of papers by Chandrasekhar and Münch (1950a, 1950b, 1951, 1952), by Münch and Chandrasekhar (1952), and by Limber (1953). More recently Peters (1970) presented an analysis of this kind based on extensive photographic observational material. Although the influence of clumpiness of the dust distribution on the mean integrated starlight was thoroughly discussed in these papers, it has not been properly included in most of the photometric models of the Galaxy. Only the models of Caplan and Grec (1979) and Mattila (1980a, 1980b) incorporate these effects.

Stellar accelerations and the galactic gravitational field

2019 ◽  
Vol 36 ◽  
Author(s):  
Hamish Silverwood ◽  
Richard Easther
Keyword(s):  
Dark Matter ◽  
Milky Way ◽  
Precision Measurements ◽  
Small Scale ◽  
Milky Way Galaxy ◽  
Newtonian Dynamics ◽  
The Galaxy ◽  
Velocity Changes ◽  
Blind Search ◽  
Stellar Motion

AbstractTypical stars in the Milky Way galaxy have velocities of hundreds of kilometres per second and experience gravitational accelerations of $\sim\!10^{-10}~{\rm m\,s}^{-2}$, resulting in velocity changes of a few centimetres per second over a decade. Measurements of these accelerations would permit direct tests of the applicability of Newtonian dynamics on kiloparsec length scales and could reveal significant small-scale inhomogeneities within the galaxy, as well increasing the sensitivity of measurements of the overall mass distribution of the galaxy. Noting that a reasonable extrapolation of progress in exoplanet hunting spectrographs suggests that centimetre per second level precision will be attainable in the coming decade(s), we explore the possibilities such measurements would create. We consider possible confounding effects, including apparent accelerations induced by stellar motion and reflex velocities from planetary systems, along with possible strategies for their mitigation. If these issues can be satisfactorily addressed, it will be possible to use high-precision measurements of changing stellar velocities to perform a ‘blind search’ for dark matter, make direct tests of theories of non-Newtonian gravitational dynamics, detect local inhomogeneities in the dark matter density, and greatly improve measurements of the overall properties of the galaxy.

VVV Microlensing events in the far side of the Milky Way

2019 ◽  
Vol 14 (S353) ◽  
pp. 35-37
Author(s):  
María Gabriela Navarro ◽  
Dante Minniti ◽  
Rodrigo Contreras Ramos
Keyword(s):  
Milky Way ◽  
The Other ◽  
Line Of Sight ◽  
Galactic Bulge ◽  
Near Ir ◽  
The Galaxy ◽  
Different Populations ◽  
First Time

AbstractIn order to study the most reddened areas of the Milky Way we used near-IR data from the VVV Survey. For the first time, the VISTA telescope allows us to observe the mid-plane through the Galactic bulge and study the disk in the other side of the Milky Way. Motivated by the detection of hundreds of microlensing events in the inner regions of the Galaxy, we propose three new configurations of microlensing events, placing the sources in the far-disk and the lenses in the far-disk/bulge/near-disk. These new configurations will change the usual way to interpret the timescale distributions due to the different populations along the line of sight, that exhibit varied transverse velocities and relative distances.

scholarly journals SYNERGY BETWEEN OPTICAL (GAIA) AND RADIO (VLBI)ASTROMETRIC RESEARCHES

2020 ◽  
Vol 52 ◽  
pp. 9-11
Author(s):  
N. Sakai
Keyword(s):  
Spatial Distribution ◽  
Milky Way ◽  
Spiral Arms ◽  
Multi Wavelength ◽  
Complex Picture ◽  
Galactic Spiral

Optical and radio astrometry have become significant for mapping the Milky Way. We introduce an example of synergy between optical and radio astrometry on a research of the Galactic spiral arms. Kinematics and spatial distribution of star and gas indicate a new and complex picture of the Galactic spiral arms. Synergy of astrometric study at multi-wavelength would be enhanced thanks to future infrared astrometric projects (e.g.,Small Jasmine; GaiaNIR) in 2020-2030s.

scholarly journals Synthetic observations of spiral arm tracers of a simulated Milky Way analog

2020 ◽  
Vol 642 ◽  
pp. A201 ◽  
Author(s):  
S. Reissl ◽  
J. M. Stil ◽  
E. Chen ◽  
R. G. Treß ◽  
M. C. Sormani ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Interstellar Medium ◽  
Faraday Rotation ◽  
Milky Way ◽  
Line Of Sight ◽  
Unit Distance ◽  
Spiral Arms ◽  
Rotation Measure ◽  
The Magnetic Field ◽  
Spiral Arm

Context. The Faraday rotation measure (RM) is often used to study the magnetic field strength and orientation within the ionized medium of the Milky Way. Recent observations indicate an RM magnitude in the spiral arms that exceeds the commonly assumed range. This raises the question of how and under what conditions spiral arms create such strong Faraday rotation. Aims. We investigate the effect of spiral arms on Galactic Faraday rotation through shock compression of the interstellar medium. It has recently been suggested that the Sagittarius spiral arm creates a strong peak in Faraday rotation where the line of sight is tangent to the arm, and that enhanced Faraday rotation follows along side lines which intersect the arm. Here our aim is to understand the physical conditions that may give rise to this effect and the role of viewing geometry. Methods. We apply a magnetohydrodynamic simulation of the multi-phase interstellar medium in a Milky Way-type spiral galaxy disk in combination with radiative transfer in order to evaluate different tracers of spiral arm structures. For observers embedded in the disk, dust intensity, synchrotron emission, and the kinematics of molecular gas observations are derived to identify which spiral arm tangents are observable. Faraday rotation measures are calculated through the disk and evaluated in the context of different observer positions. The observer’s perspectives are related to the parameters of the local bubbles surrounding the observer and their contribution to the total Faraday rotation measure along the line of sight. Results. We reproduce a scattering of tangent points for the different tracers of about 6° per spiral arm similar to the Milky Way. For the RM, the model shows that compression of the interstellar medium and associated amplification of the magnetic field in spiral arms enhances Faraday rotation by a few hundred rad m−2 in addition to the mean contribution of the disk. The arm–interarm contrast in Faraday rotation per unit distance along the line of sight is approximately ~10 in the inner Galaxy, fading to ~2 in the outer Galaxy in tandem with the waning contrast of other tracers of spiral arms. We identify a shark fin pattern in the RM Milky Way observations and in the synthetic data that is characteristic for a galaxy with spiral arms.

scholarly journals The 3-Dimensional Distribution of Interstellar Dust

2013 ◽  
Vol 9 (S298) ◽  
pp. 213-220
Author(s):  
Jayant Murthy
Keyword(s):  
Interstellar Dust ◽  
Three Dimensional ◽  
3 Dimensional ◽  
Dust Extinction ◽  
Structure And Morphology ◽  
Current State ◽  
The Galaxy ◽  
Dimensional Distribution ◽  
Color Data ◽  
Dust Distribution

AbstractA knowledge of the three dimensional distribution of interstellar dust is critical in interpreting all observations of the sky, particularly in the understanding of the structure and morphology of our Galaxy. It has been much easier to map the integrated dust extinction through the Galaxy, which is needed in modeling extragalactic sources, but this yields an overestimate of reddening to Galactic objects. Massive surveys, such as Gaia, present both a problem in that the distribution of interstellar dust must be known in order to model the internal structure of the Galaxy and an opportunity in that multi-color data may be used to deconvolve the dust distribution. I will present the current state of the modeling, which is yet in its early stages.

Progress on 21 cm Studies of the Southern Milky Way _

1975 ◽  
Vol 2 (6) ◽  
pp. 364-365 ◽  
Author(s):  
F.J. Kerr
Keyword(s):  
Milky Way ◽  
Spiral Structure ◽  
Radial Velocities ◽  
Straightforward Manner ◽  
Spiral Arms ◽  
Distance Transformation ◽  
Galactic Spiral Structure ◽  
Structure Problem ◽  
Galactic Spiral

In the first decade or so of 21 cm studies the galactic spiral structure problem was treated in a very straightforward manner. A simple velocity-distance transformation was used to derive the locations of the spiral arms from the radial velocities of the main features on the 21 cm profiles. Some well-known diagrams were obtained in this way.

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