Galactic Radio Astronomy by Yoshiaki Sofue

Author:Yoshiaki Sofue
Language: eng
Format: epub
Publisher: Springer Singapore, Singapore

In the bottom of Fig. 4.17, we show the most recent face-on map of the column density of HI (red) and H2 (green) gases in the Milky Way. Shown together are a vertical cross-section of the Milky Way in the plane including the galactic center. These maps were obtained from the 3D distribution map of the Milky Way constructed using the HI and CO line observations.

4.3.5 dv∕dl Method to Measure Distances to Arms in the GC Direction

In the VST method to map the Milky Way’s face-on view, the region near the GC-Sun line (l ∼ 0∘ and ∼ 180∘) is the singular region where the distance equation cannot be applied because of the degeneration of the radial velocity to zero. In this particular region, there is a special method to use the gradient of the LV ridge as the distance indicator. Figure 4.18 illustrates longitude gradients in the LV diagram and corresponding arms and rings, an example of the observed LV diagram in the CO line near the galactic center.

Fig. 4.18Gradients dv r∕dl of arms and rings traced on the longitude diagram around l ∼ 0∘ are used as a distance indicator [3]

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