After I posted my two part blog series comparing the latest parallax-based distance estimates with my model of the Milky Way for the inner galaxy and the Perseus arm, Winchell Chung drew my attention to news coverage of an Urquhart, Figura et.al. arXiv preprint analysing red MSX sources (RMS) - HII regions and massive young stellar objects visible in the MSX infrared survey.
Like the recent parallax results, the RMS paper displays distance estimates overlaid on Robert Hurt's image of the Milky Way. There are two major differences from the parallax results, however:
- the RMS results cover almost the entire galaxy with the exception of the bar and ring (3 Kpc arms), and
- most of the distances were estimated from kinematic and spectrophotometric data rather than using the more reliable parallax method.
As the RMS paper points out, parallax-based estimates are not possible for most of the galaxy because the data is not yet available.
I have taken the RMS/Hurt image from the paper (Figure 6) and overlaid it on my model. The colours in figure 6 are inverted in this illustration, and hence in this version, complexes of HII regions and massive young stellars objects are represented by blue circles and individual sources by red circles.
A larger 2324x2168 version of this image is available here.
There are many interesting features about this image. I'll highlight some in the fourth quadrant in my next blog post.