Science Online: The Good, the Bad and the Crazy

In 2010, astrophysics professor Pavel Kroupa at the University of Bonn – he of the stellar Initial Mass Function - published a paper in which he highlighted problems with the Standard Model of Cosmology (the so-called ΛCDM model, of which cold dark matter is a crucial ingredient), particularly in its predictions related to environments of large spiral galaxies. In a provocative move, he cited the discrepancies between the model’s predictions and observations as evidence that ΛCDM “doesn’t work”, and that we should explore alternative theories. One of these alternatives is Modified Newtonian Dynamics, or MOND.

In the months after the publication, the University of Bonn hosted a debate on this thorny subject between Kroupa and one of the architects of the ΛCDM framework, Simon White, Director of the Max Planck Institute for Astrophysics in Garching. I thought this was an excellent idea, wrote a few blog posts about the matter and posted the live blog and video of the debate.

To those that read or watched the debate, it was clear that the two scientists don’t disagree in a fundamental way - ΛCDM has proved an extremely successful framework for cosmological structure formation, but the dwarf satellite problem is generally acknowledged. Kroupa’s most important point is that the community should not ignore those observables that don’t match the predictions of ΛCDM, and he encourages scientists not to get locked into a “cold dark matter” mindset, but to explore entirely novel theories, of which MOND is one example. This discussion has been expanded and illustrated further in a blog run by Marcel Pawlowski, a member of Kroupa’s group in Bonn, the Dark Matter Crisis, now hosted on SciLogs.com, which is run by Nature and the German edition of Scientific American.

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Small galaxy, Massive black hole

Tomorrow’s edition of Nature contains an interesting astrophysics paper that I must blog about for the sake of domestic peace and harmony. It’s commonly accepted that all galaxies contain a massive black hole at their centre. Measuring the masses of these black holes is tough, but those we’ve been able to make that measurement for show a strong correlation between the black hole mass and that of the total mass of stars in the galaxy. This suggests that somehow the evolution of a galaxy and that of its central black hole are intricately linked, and this is now a key given in our understanding of galaxy evolution.

This new paper, by Remco van den Bosch here at MPIA and a number of collaborators, now convincingly challenges this assumption. In a large survey of very massive nearby galaxies with the Texan Hobby Eberly Telescope, they discovered a number of galaxies that appear to contain black holes whose mass dominates their total stellar mass. For one of these, the team obtained much additional data to rule out any problems with their original data or the methods used to derive the black hole mass. This galaxy, NGC 1277, is the subject of the paper.

NGC 1277 is definitely an interesting galaxy, but on its own cannot change these long-held assumptions. After all, every population has its outliers. What’s particularly exciting is that there appear to be others like it.

I’ve watched this paper in the making over the last few months, years even, and while it’s not my work, I’m quite proud to see it in print and receiving attention in so many places. Congrats to the authors and well done for the hard work.

van den Bosch et al, An over-massive black hole in the compact lenticular galaxy NGC 1277, Nature 2012 (paywalled) – or astro-ph. [links added, 29/11/12]

 

A Faculty Address | profserious

Anthony Finkelstein, Dean of the UCL Faculty of Engineering Science and tweeter,  wrote a fictitious and pastiche-y commencement address for new graduates on his blog, which I rather like.

Ladies and Gentlemen of the Class of 2012. Use statistical quality control. If I could offer you only one tip for the future, statistical quality control would be it. Scientists and engineers have shown that by careful sampling and testing you can ensure the quality of a product. The rest of my advice has no basis more reliable than my own meandering experience. I will dispense this advice now.

Undertake further formal education. I understand, you are fed up with education and with the exam treadmill. But trust me, in 20 years, you will look back and comprehend how little of what there was to know we have had the opportunity to teach you.

Your maths is better than you think.

Plan your career. Just understand that the real career opportunities arrive, out of the blue, in the email at 5.30 on a Friday evening. Be ready to take them.

Read the whole text here.

via Software Engineering Distilled | profserious.

Star formation near and far

 

Artist’s impression of the face-on structure of the Milky Way galaxy with the names of the spiral arms indicated.

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.

Longitude-velocity plot of the CO gas in the Milky Way Galactic plane, with bubble locations overplotted. Click to enlarge.

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.

Some references

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

Champagne and Chocolate

Many of my recent blog posts have all been about Milky Way Project, and there’s a good reason for that. The publication of our first paper, which is in press at the moment with Monthly Notices, was just a first big milestone, with more to come. I’m currently writing a follow-up paper using the initial data catalogues, and as I’m scheduled to give a talk about it at the end of the month at the joint UK/German National Astronomy Meeting in Manchester, I’d better make a move on with getting the results out.

The paper won’t be the photogenic blockbuster that Rob wrote for us,  but just in case you don’t share my histogram-fetish (… you simple soul!), I’ve managed to find space for one rather sexy bubble picture to add a bit of spice. If and when the paper gets accepted I’ll instruct the editor to place it on Page 3.

My own data adventures aside, this week was another heap of fun for the project. NASA put out a press release to mark the first data release. It didn’t get picked up in too many places – there was Astronomy Magazine, Space.com, and also a short piece in the Mail Online with obligatory pretty pics of the Spitzer images and our MWP heat maps. The Mail upped Eli Bressert’s “champagne bubble” quote to liken the Milky Way to a nougat-y chocolate bar.

If I’m being a pedantic scientist, I should add that neither of those analogies are actually very accurate. Champagne bubbles are maybe somewhat similar in that they’re lighter than the liquid they’re in, but our interstellar bubbles aren’t thought to be floating or rising through the interstellar medium. But they do expand. As for chocolate bars… No, that doesn’t work either.

At Milky Way Project HQ, we launched a new phase of the project. While we continue to collect your ‘regular’ bubble drawings, we’ve now added close-up images of bubbles that are already in the catalogue, for which we’re trying to get more precise sizes and thicknesses. Rob explains all here. Our drawing tools were fairly coarse, as some users had remarked, particularly for drawing smaller bubbles. So with these new images we will try to gather more precise measurements.

I’m really looking forward to the NAM conference later this month. I haven’t been to one of these meetings since the first year of my PhD (Dublin!), and they’re great for catching up with old friends and colleagues. Having it joint with its German equivalent meeting (the AG) means that both old and new friends will be at the meeting. Another factlet is that I’m actually half-Mancie, and although my association with the city is pretty patchy (what, you haven’t noticed my striking Northern accent?), it’s fun to be there.