This week our astronomy colleagues at the University of Heidelberg are hosting a conference on Galactic Scale Star Formation here in Heidelberg, and what a treat it is to be able to attend this week-long event so close to home. So far there’s been lots of good talks showing data from recent large-scale surveys of the Galactic plane, such as ATLASGAL and the Bolocam Galactic Plane Survey in the (sub-)millimetre and HiGAL in the far-infrared, and also some great talks on star formation in other galaxies. The Galactic plane surveys form the perfect complement to the Spitzer surveys GLIMPSE and MIPSGAL, so at Milky Way Project we’re big fans already.
I presented some of my recent work with our Milky Way Project bubbles in yesterday morning’s session. I gave a whirlwind tour of our recent statistical analysis paper (just this week published in the Astrophysical Journal), and showed a few things I’ve been working on recently to address some uncertainties in the analysis: the distances to the bubbles in our sample, and the evolutionary degeneracy we came up against with the RMS survey data used for the correlation analysis.
The main idea is to tighten up the results we presented in the paper and perhaps show some stronger evidence for star formation being sparked in the vicinity of expanding bubbles all over the Galaxy. But from the many questions and comments I received yesterday after the talk it’s clear that such correlations of large scale surveys at different wavelengths, and the ability to place objects in 3D space in the Galaxy, are really useful for improving our understanding of Galactic star formation in general.
It’s very pleasing that Milky Way Project is getting such an enthusiastic reception in the community! I’m itching to get on with more follow-up work now.
After spending a couple of days cross-matching our MWP bubbles with catalogues of HII regions (from Anderson & Bania 2009 in black and Anderson et al 2012 in red) and stellar clusters (from Morales et al, in preparation, in orange), whose velocities have all been measured, I plotted the corresponding velocities onto the composite longitude-velocity (LV) map of the CO gas in the Galaxy, produced by Dame et al in 2001.
Incidentally, measuring the distances to objects in our own Galaxy is a real pain, so I’m delighted that others have already put in so much hard work on that subject. Just yesterday Yancy Shirley of the University of Arizona gave a talk about his work on measuring distances to BGPS clumps, for which he has to visually inspect ~25,000 (if I remember the ridiculously large number correctly) radio spectra.
In any case, this LV map shows the different velocity components of the molecular gas in our Galaxy against galactic longitude. If you imagine looking through the plane of the Galaxy, gas at different distance will be seen to travel at different velocities either towards or away from the Sun, and that’s what is visualised in a longitude-velocity plot.
It’s particularly useful for tracing large scale structure in the gas distribution, particularly the spiral arms where most of this gas is concentrated. In this case, we can see that the bubbles generally trace the molecular gas very nicely, and our users have even identified some bubbles beyond 15 kpc, in the Outer Arm of the Galaxy. With apologies to Rob’s student, there’s a new “Most Distant Bubble” in town! This plot is very preliminary though and needs much more work to be properly robust.
There are interesting things to learn from this plot, and of course we have around 10 times more bubbles to add than are shown in this plot. I’m learning as I go along as well, hopefully more exciting results to write about and publish in the near future.
L. D. Anderson, & T. M. Bania (2008). Resolution of the Distance Ambiguity for Galactic HII Regions Astrophys.J.690:706-719,2009 arXiv: 0810.5570v1
L. D. Anderson, T. M. Bania, Dana S. Balser, & Robert T. Rood (2012). The Green Bank Telescope HII Region Discovery Survey: III. Kinematic
Distances ApJ, 754 (1) arXiv: 1205.4228v1
T. M. Dame, Dap Hartmann, & P. Thaddeus (2001). The Milky Way in Molecular Clouds: A New Complete CO Survey Astrophys.J. 547 792-813 arXiv: astro-ph/0009217v3
Sarah Kendrew, Robert J. Simpson, Eli Bressert, Matthew S. Povich, Reid Sherman, Chris Lintott, Thomas P. Robitaille, Kevin Schawinski, & Grace Wolf-Chase (2012). The Milky Way Project: A statistical study of massive star formation associated with infrared bubbles ApJ , 755 (1) arXiv: 1203.5486v2