94. The Galactic System as a Spiral Nebula

Oort, J. H.; Kerr, F. J.; Westerhout, G.

doi:10.4159/harvard.9780674366688.c101

Cited by 71 publications

(90 citation statements)

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“…This structure was first identified in our Galaxy with observations of H I (Oort et al 1958) and was first clearly delineated by Georgelin & Georgelin (1976) using kinematic distances of H II regions supplemented by optical observations of massive stars. Many other tracers such as CO emission, especially from giant molecular clouds (e.g., Grabelsky et al 1988) and methanol masers (e.g., Green et al 2011) have helped to define the spiral structure.…”

Section: Spiral Armsmentioning

confidence: 99%

A New Electron-Density Model for Estimation of Pulsar and FRB Distances

Yao¹,

Manchester²,

Wang³

2017

ApJ

1,055

997

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We present a new model for the distribution of free electrons in the Galaxy, the Magellanic Clouds, and the intergalactic medium (IGM) that can be used to estimate distances to real or simulated pulsars and fast radio bursts (FRBs) based on their dispersion measure (DM). The Galactic model has an extended thick disk representing the so-called warm interstellar medium, a thin disk representing the Galactic molecular ring, spiral arms based on a recent fit to Galactic H II regions, a Galactic Center disk, and seven local features including the Gum Nebula, Galactic Loop I, and the Local Bubble. An offset of the Sun from the Galactic plane and a warp of the outer Galactic disk are included in the model. Parameters of the Galactic model are determined by fitting to 189 pulsars with independently determined distances and DMs. Simple models are used for the Magellanic Clouds and the IGM. Galactic model distances are within the uncertainty range for 86 of the 189 independently determined distances and within 20% of the nearest limit for a further 38 pulsars. We estimate that 95% of predicted Galactic pulsar distances will have a relative error of less than a factor of 0.9. The predictions of YMW16 are compared to those of the TC93 and NE2001 models showing that YMW16 performs significantly better on all measures. Timescales for pulse broadening due to interstellar scattering are estimated for (real or simulated) Galactic and Magellanic Cloud pulsars and FRBs.

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Section: Spiral Armsmentioning

confidence: 99%

A New Electron-Density Model for Estimation of Pulsar and FRB Distances

Yao¹,

Manchester²,

Wang³

2017

ApJ

1,055

997

View full text Add to dashboard Cite

show abstract

“…Because of the far distances involved and the warp of the Galactic plane from the solar radius outwards (e.g., Burke 1957;Oort et al 1958;Henderson et al 1982), an unbiased Galactic plane CO survey with the combination of high-sensitivity, wide latitude coverage, and wide velocity coverage is essential for the discovery of more EOG clouds. The Milky Way Imaging Scroll Painting (MWISP) project is a high resolution (50 ′′ ) J = 1-0 12 CO, 13 CO, and C 18 O survey of the northern Galactic Plane, performed with the Purple Mountain Observatory Delingha 13.7 m telescope.…”

Section: Introductionmentioning

confidence: 99%

Molecular Clouds in the Extreme Outer Galaxy between l = 34.°75 to 45.°25

Sun

Zhang

et al. 2017

ApJS

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We present the result of an unbiased CO survey in Galactic range of 34.75• ≤l≤ 45.25• and -5.25• ≤b≤ 5.25• , and velocity range beyond the Outer arm. A total of 168 molecular clouds (MCs) are identified within the Extreme Outer Galaxy (EOG) region, and 31 of these MCs are associated with 13 CO emission. However, none of them show significant C 18 O emission under current detection limit. The typical size and mass of these MCs are 5 pc and 3×10 3 M ⊙ , implying the lack of large and massive MCs in the EOG region. Similar to MCs in the outer Galaxy, the velocity dispersions of EOG clouds are also correlated with their sizes, however, are well displaced below the scaling relationship defined by the inner Galaxy MCs. These MCs with a median Galactocentric radius of 12.6 kpc, show very different distributions from those of the MCs in the Outer arm published in our previous paper, while roughly follow the Outer Scutum-Centaurus arm defined by Dame & Thaddeus (2011). This result may provide a robust evidence for the existence of the Outer Scutum-Centaurus arm. The lower limit of the total mass of this segment is about 2.7×10 5 M ⊙ , which is about one magnitude lower than that of the Outer arm. The mean thickness of gaseous disk is about 1.45• or 450 pc, and the scale height is about 1.27• or 400 pc above the b = 0 • plane. The warp traced by CO emission is very obvious in the EOG region and its amplitude is consistent with the predictions by other warp models using different tracers, such as dust, HI and stellar components of our Galaxy.

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“…Distances of the various features or objects are derived through a kinematical model, with near-far ambiguities inside the solar circle. The first deprojections of the Galactic plane in the atomic gas observed at 21cm (Oort et al 1958 [21]) had only a very sketchy and approximative spiral morphology, without identifying the actual arms, and their continuity. One of the first successful models was that from Georgelin & Georgelin (1976) [14] of four tightly-wound arms, traced by OB associations, optical or radio HII regions, or molecular clouds.…”

Section: The Importance Of the Gasmentioning

confidence: 99%

Molecular gas and star formation in the Milky Way

Combes

2012

EPJ Web of Conferences

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Abstract. The dense molecular gas is the ideal tracer of the spiral structure in the Milky Way, and should be used intensively to solve the puzzle of its structure. In spite of our position inside the plane, we can hope to disentangle the structures, with position-velocity diagrams, in addition to (l − b). I summarize the state of the art simulations of gas flows in the MW, and describe what can be done to improve the models, taking into account the star formation, in view of what is already done in external galaxies, with a more favorable viewing angle.

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94. The Galactic System as a Spiral Nebula

Cited by 71 publications

References 0 publications

A New Electron-Density Model for Estimation of Pulsar and FRB Distances

A New Electron-Density Model for Estimation of Pulsar and FRB Distances

Molecular Clouds in the Extreme Outer Galaxy between l = 34.°75 to 45.°25

Molecular gas and star formation in the Milky Way

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