Follow the reluctant adventures in the life of a Welsh astrophysicist sent around the world for some reason, wherein I photograph potatoes and destroy galaxies in the name of science. And don't forget about my website, www.rhysy.net



Sunday, 28 October 2018

Strictly Come Strasbourg Science Seminaring

Hey look, a travel post ! Remember those ? I keep forgetting to write them.

3:30 is not a time that should ever occur in the morning, and if it does, it should only happen because of pub-related shenanigans. Unfortunately, if I wanted an expenses-paid trip to Strasbourg to give a seminar (which I did), I'd have to both avoid the pub and haul my sleep-deprived self out of bed at that ungodly hour onto a plane. Worse for me is that as well as being too paranoid to risk getting the 5am metro to catch a 6:30am flight, I'm so paranoid about missing flights that I barely slept at all. Though sunrise from a plane is always nice, even if you're heavily sleep deprived and irrationally scared of missing flights that someone else has paid for.


Toward the end of the second, mercifully uneventful flight, the little jet descended from the rosy dawn into the grey gloom of Strasbourg.


By Welsh standards, this weather - i.e. not raining - is positively delightful. And it got better later on anyway. From the airport so small you could practically spit from one side to the other, it was a simple ten minute train ride to the city centre station. Which is from the inside an interesting mix of classical and modern architecture, though from the outside is a ghastly monstrosity. It looks a bit like what would happen if you took a graffiti artist, a leading bubble wrap manufacturer, shoved them in a room together and gave them too much money.


Since my seminar wasn't until the next day, I decided to walk to my hotel and see a little of the city before doing anything sciencey. Strasbourg is not quite in the same league as Prague, but comparing any city* to Prague is a bit like comparing landscapes to Switzerland : it's just not fair. By more reasonable standards, Strasbourg is a lovely place with many fine buildings, a nice, compact historic city centre, and very easy to navigate.

* Except Cardiff, obviously.





What I also noticed was that the cyclists put those of Prague to shame. Prague cyclists are all damned aggressive bastards who delight in obnoxiously taunting innocent pedestrians. Yes, all of them. Every. Single. One. They'd probably prefer to mangle themselves and their infernal contraptions in your gizzards than move an inch out of their god-given right of way, preferring to suffer an extended hospital visit than grant a pedestrian the merest moment of admission that they might be at a fault. I, for one, don't like them.

Anyway, Strasbourg cyclists are to be commended. They know that cycle lanes can also be used by pedestrians and aren't always clearly marked. They don't give you any grief if you happen to be in their way. They just quietly and calmly flow around you like a shoal of elegant French fish, and if they have to wait, then so be it. They are truly an inspirational example to us all.

I got to my hotel too early to check in, so I went off to the Observatory instead. This is a grand, historic building, a little complex of old telescopes of various sizes, a planetarium, some gardens with a vegetable patch and even beehives. It's like a little country estate nestled inside the city.



Once you go in through the grand entrance, the first thing you see - the very first thing - is this :


Charming. The sort of thing that would probably be blocked by Facebook's filters, I expect. On the other side is an old wooden telescope, but what the statue's for is anyone's guess. Perhaps it's a sculpture of the unusually hunky astronomer who used to use said telescope. Regardless, it's an impressive building.


My invitation came from Frédéric Marin, friend, colleague, and former housemate. Frédéric's expertise is mainly in X-ray polarimetry of active galactic nuclei. In real terms that means looking at the X-ray emission from the searingly hot gas that orbits supermassive black holes, trying to determine the structure of the gas by other means than resolving it directly because that's fiendishly hard. This relies on relativistic, very high energy physics that's quite different to my own field of nice, sedate hydrogen clouds that don't do anything.

Frédéric also works on Space Nazis studying multi-generational spaceships, looking at how a small population could ensure it was genetically healthy over many centuries. He's found that the smallest number that could reliably ensure everyone didn't die out because of Lannisterism / they had eighteen fingers on each hand or seven malformed penises / inbreeding is about a hundred. More on that in a future post, as we're collaborating on a (submitted) paper about the farming requirements of the Space Nazis colonists.

(I'm exaggerating the eugenic overtones of the necessary breeding program. It turns out the situation wouldn't be all that bad : you would need some breeding restrictions, but actually not that limiting compared to the choices people naturally make anyway)

So we caught up on life, the Universe and everything for a while, discussing the bizarre hiring system for permanent academics in France, possible ALMA observations, that sort of thing. Frédéric is a ridiculously competent, hugely energetic and multi-talented guy who, at 32, is even managing the development of his own satellite. I kid thee not, it's absolutely mental. Then the near-total lack of sleep caught up with me and, fearing that I was about the headbutt the desk as I continuously dozed into mild hallucinations, I went back to my hotel for a very rare mid-afternoon nap. After that I spent considerable time wandering around the nicer bits of Strasbourg, and luckily for me the Sun had come out. Not in the sexual sense though, which was good because that would be really weird.





Of course, no visit to Strasbourg would be complete without seeing its world-famous cathedral with its 143m spire. Fortunately I didn't have to turn back because of snow. Unlike some other churches, it's a genuinely impressive, absolutely monumental mass of gothic stonework. Even after living in hundred-spired Prague, it's well worth a look.





Since time was finite, I decided to spurn the interior and went off to see some more of the city. I think that was a wise choice. Strasbourg struck me as an all-round charming little place, appealing both for tourists and residents.





And so the next day I gave my seminar, which went without a hitch. Normally I practise seminars excessively, repeating them to an empty room at least ten times before daring to speak to an audience, especially one of experts (given that seminars are usually at least 45 minutes long, I'm not sure people always appreciate the time commitment they're requesting when they ask me for a presentation). Fortunately this one was different : I recycled most of it from previous, recent talks, and after only three or four iterations I realised I could say this stuff in my sleep, possibly while gagged and drugged. It was, of course, about the usual stuff, mostly dark galaxy candidates and their alternative explanations.

I was a little wary that the audience might be more hostile than usual. Strasbourg may be a small city but its astronomy group has a lot of prestigious names, and features a lot of outside-the-box thinkers researching modified gravity, planes of satellites, that sort of thing. Regular readers know I'm not exactly keen on those. And the Observatory director is none other than Pierre-Alain Duc, who produced one of the most influential models demonstrating that dark galaxy candidates could be tidal debris.

(I'm not going to try and summarise the science this time, you'll have to consult the links. The rest of this post is mainly for enthusiasts.)

But the lions in this particular lions den turned out to be an affable bunch. There were some questions during the presentation and about 15 minutes of discussion afterwards, all perceptive and relevant. Duc couldn't attend but we had a private discussion for about 30 minutes or so later on. And that was useful too.

One point that keeps being raised about these dark clouds is whether their high spectral line widths could be explained by their actually being several different clouds that are all at the same position but at different distances along our line of sight. I'm confident that this can't be the case. First, there are hardly any such clouds known at all, so the chance of coincidental alignments of multiple clouds is negligible. Second, higher spectral resolution observations don't show any evidence of multiple spectral components. Third, having a series of such clouds along the line of sight but still no connections to nearby galaxies would probably make these things harder to explain, not easier.

So I think I managed to convince people that these things are at least interesting. I'm not at all sure what they actually are, and I played that card very strongly. While I still have some reservations, I lean heavily towards accepting the system that Duc modelled probably is a result of tidal encounters, even if that's not the whole story. But all such clouds ? I very much doubt it. The general view seemed to be that the high-resolution VLA data we've obtained ought to be enough to settle the matter. And my goodness, I'd like to reduce that data but it's a matter of finding time/assistance.

Duc raised a couple of points I wasn't previously aware of. One is that other ultra-diffuse galaxy candidates people have claimed to have hydrogen detections have turned out not to be galaxies at all, but more ragged stellar patches for which the traditional parameters are misleading (like using the mean when you should be using the median, only worse). They are, he says, more likely to be tidal dwarfs than giant galaxies. Though I think the ones we've found, which have enormous amounts of hydrogen with nice clear classical double-horn profiles and continuous stellar discs, are probably much more secure. So I'm confident that a possible connection between very faint galaxies (which we know exist) and optically dark, gas-rich galaxies (for which we have only candidates) is still very plausible. That's extra motivation to publish our observations.

His second point concerns Keenan's Ring. He notes that off-centre rings can indeed be produced by galaxy-galaxy collisions, for example the case of NGC 2992 :
From Duc et al. 2000. Hydrogen contours are overlaid in green on an optical image.
He also notes that the velocity difference from Keenan's Ring and M33 is not so great (~200 km/s or thereabouts). These are good points, and I wasn't aware of the the NGC 2992 system. But could Keean's Ring be something similar ?

I'm skeptical. The ring in NGC 2992 is clearly connected to its parent at two points - no such connection is evident for Keenan's Ring. The NGC 2992 ring is found at identical velocities to its parent galaxy, whereas Keenan's Ring is at completely different velocities with no evidence of any overlap. The colliding galaxy in the NGC 2992 system is obvious, and there's a strong stellar disturbance as well - neither of which is evident for Keenan's Ring. Finally, Wright's Cloud is also close to M33, and it would be a heck of a coincidence if this was unrelated to the Ring - and no such analogue is found in the NGC 2992 system. It's certainly intriguing and that's given me some reading to do, but my immediate feeling is that the differences outweigh the similarities. I don't think we're going to make much progress here without really deep data over a much wider area than we currently have.

In the end, I don't think I managed (or even wanted) to convince anyone that I'd made some shattering discovery or that I had stunning evidence for some alternative theory. But I'd set myself the more modest goal of persuading people that these objects are interesting and worth investigating, and in that I hope I was successful.

There, a post that isn't five hundred pages long and contains a bare minimum of ranting. Don't worry, normal services will be resumed as soon as possible.

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