At the IRAM 30 m telescope

This post is edited from a series of updates I originally posted on Google Plus. I decided the best way to archive it would be to reduce it down to the highlights.


Getting there

Stage one of my journey is complete. I've made it to Granada without losing my luggage. The one thing they don't tell you on the "Getting to the telescope" instructions page is that the after-hours guard is one of those very enthusiastic people who thinks that any language can be understood by anyone, as long as it's spoken loudly and with expressive hand gestures. They also don't tell you that the sign for the guest room is very hard to see in the dark, or where exactly the building is in the quite large gated complex of apparently random other buildings. I spent about 15 minutes wandering around randomly before I gave up and asked some passers-by where the hell I was going. That involved another 10 minutes with the guard - dunno why, if you know where the building is it isn't that hard to find.

Oh well, as escapes go, I've had much worse. Tomorrow it's an 8am start to get to Pico Veleta site. I've been promised that this involves a vehicle with caterpillar tracks.


Arrival

I've made it to the telescope. Fantastic views of the Sierra Nevada as we came up, but the snow moved in almost as soon as we arrived. Visibility outside is now down to ~10 metres. Didn't get to ride the snowmobile because there wasn't enough snow on the road. Looks like that might change... observations are on hold until Friday because of the weather.

My room at the telescope doesn't come with a view, but only because it's snowing and blowing a gale right now. But it does come with a treadmill and and a TV because I got lucky enough to get one of the staff scientist's rooms. Lunch even came with cheese and wine. I could get used to this... well, probably not running on the treadmill at 2850 metres, that would just be silly.


The Fox

Well I was going to just post a nice view now that there's a gap in the clouds, but then this happened. The fox was visible from the dining room, sat nearby. When he saw me he ran over and just sat there waiting for food. Still blowing a gale out there, but this little guy has the world's fluffiest coat to stay warm.

When the clouds cleared

The weather is spotlessly clear, about -10 C and with wind speeds up to 25 mph blowing loose ice crystals all over the place. Ball-freezingly cold, but worth it. So trips outside have been limited to about a minute before I admit defeat (I can't be bothered to get my coat and hat, and I've got to keep an eye on the observations anyway). The fox doesn't seem to mind it though.

Today I ventured a little further afield - enough to need a coat. :) Actually at first I wore crampons, but they proved unnecessary. I didn't go very far, though, because as you can hopefully see, these are not the sort of slopes to mess around on. Especially not at 2850 m altitude. It doesn't seem to bother the horses, but God knows what they're doing up here when there's nothing to eat. And the skiers fly around effortlessly. Which is a very strange thing to see at a radio telescope

One of the advantages of doing long integrations is that there's plenty of time to wander around. Seeing that the nearby "road" was now accessible by walkers, I had a quick venture out to get some shots of the telescope at a slightly greater distance. The artsy-fartsy lines on the ground are from where a snowmobile has been making the road more passable. The chunks of ice on the ground fell off the telescope, and they're quite a bit bigger than they appear here - which is yet another reason I'm spending almost all the time inside. Still, tomorrow I think I need to wander a little bit more....

The observing seems to be going pretty smoothly. It looks like a lot to do at first, but actually (as usual) it's just repetitively running a set sequence of commands and waiting. I only have to intervene every 30 minutes or so, less even.

All of this is to get a spectrum. This is my first stab at processing molecular data, and it's a nice clear non-detection. Not too surprising since this galaxy was a weak detection with Arecibo. For comparison, we detected it with Arecibo in 5 minutes at the neutral hydrogen line, but only weakly. Looking for molecular hydrogen (using the much weaker CO line) with a 30 m telescope, we're spending ~5 hours observing the target but it's not surprising that we're not detecting anything. Especially having talked to the other on-site observers doing a similar project and getting similar results - it seems these particular galaxies just don't have much molecular gas (for whatever reason). But this was our weakest target - the others (currently running one now) might fare better, though I suspect this will be a non-detection exercise. That becomes interesting if the sensitivity is high enough, but for that I need to learn how to calibrate the data. One thing at a time...

The targets are ultra diffuse galaxies. Forget the gas for the moment : they're about the same size as the Milky Way, but optically 100-1,000 times fainter. Here's a lengthy summary (feel free to skip).

We selected these particular targets by a complete fluke. By coincidence, a Chinese team (who I've never heard of before) did a search for UDGs in an area of the Pegasus group/cluster and published their catalogue... which just so happened to coincide with part of the AGES survey of atomic hydrogen gas. Three of our hydrogen detections are unambiguous matches to their catalogued UDGs, and that's what we're looking at with IRAM.

The amount of atomic hydrogen in these things isn't small. In fact it's comparable with (maybe even slightly larger than) the Milky Way. They are weak detections only because they're quite distant. About a hundred or so objects like this have been detected via 21 cm emission.

But the amount of molecular hydrogen is as yet completely unknown. An increasing amount of theoretical and observational evidence suggests that it's the (much colder) molecular gas which actually forms stars - the generally warmer atomic gas has too much thermal energy to collapse (this is simplifying hugely, but is basically correct).

That's where IRAM comes in. Because H2 doesn't emit directly, we use the CO line as a tracer. That requires higher frequencies, which necessitates a smoother, more accurate surface of the reflector. Hence telescopes operating at these mm wavelengths have to be much smaller and therefore less sensitive, plus (IIRC) the line is intrinsically weaker anyway. So whereas we can get a halfway-decent, though not brilliant, detection with Arecibo at 21 cm in 5 minutes, with IRAM at ~1mm we're spending ~5 hours on source. And so far neither myself nor the other team have got any detections. Just how significant this is really needs proper calibration to place a mass-sensitivity limit on the observations.

Provisionally, it looks like these objects have for some reason done a lousy job of converting their atomic gas into molecular gas. If this is correct (and it might not be !) then we have to work out why these objects manage to form a few stars, whereas other objects of similar total and atomic mass are so much more efficient. It's fun stuff, but complicated.


The journey down

I made it down the mountain via snow cat, cable car, and normal car. Snow cats are even more cool than riding in the back of a pickup truck. And now I'm in Granada, which is a heck of a travel shock for < 2 hours of travelling. Off to see if I can visit the Alhambra now...

The snow cat was the most fun part of the trip, but the cable car had the most memorable images. With giant snow blowers lining the slopes for many miles down the mountain, I was struck by the awesome, sheer industrial scale of the ski slopes. All of this energy blasted across the mountainside so that people can slide down the snow on boards strapped to their feet. With the plumes of snow illuminated by the sun, the whole thing reminded me of a colder, less dystopian version of Blade Runner. And then I finished off by visiting the Alhambra and reflecting on just how surreal the whole experience was.