Preparing for the VLA

So I've submitted my "scheduling blocks" to the VLA to get better resolution images of these optically dark hydrogen clouds in the Virgo cluster. With Arecibo they are single pixels : we get their maximum size and direct measurements of their position, mass and velocity width, but that's all. That's enough to say, "these little buggers are very interesting", but not enough to determine what the hell they actually are. We can run simulations for years and years, but we'll never really know without more data.

These observations will get us resolution that's about 4x better than Arecibo - not a huge gain, but potentially enough to distinguish between possible explanations. Given their mass we can work out a lower size limit at which they should have a density high enough to form stars - if they're close to that we'll know if we've caught them at a strange phase in their evolution just before they ignite star formation. In that case we might consider searching for molecular hydrogen. Or they might be more extended, rotating objects which could be stable on long timescales, in which case that's probably a Nature paper. Tonnes of stuff we can potentially get from this.

Of course, we'd like even better resolution, but that's not so easy. Interferometers like the VLA have sensitivity effects that single-dishes like Arecibo just don't have - making them (in some situations) far worse than due to the difference in collecting area. So their sensitivity to diffuse gas is ~100-1000x lower, and while these clouds were detected at Arecibo in 5 minutes of observations, we've requested 2 hours for each one at the VLA. Even then, since we don't know the true structure of the clouds, we're not guaranteed to detect anything. Fingers crossed...

Reading the VLA observing guide and links therein has been a less than fun affair, much like reading an old computer manual. Great if you need reference info, not so good if you need to learn stuff for the first time. The sheer amount of information is mmmmwwwaaaaaarrrgh. It takes a lot of getting used to the different terminologies : "scheduling block" really mean "observing script", "resource file" really means "telescope configuration file". I wouldn't say these are particularly intuitive labels and it makes mentally processing the information very much harder than it needs to be.

On the positive sides, the observing preparation tool is very nice. It's a simple, reasonably intuitive GUI webpage rather than a scripting language like Arecibo uses (though Arecibo does have an interactive GUI for doing the observations too). And even better, the NRAO helpdesk is genuinely very, very helpful, responding to my inept inquires in a few hours and in great detail.

And so now we play the waiting game, until the data arrives and I have to learn how the heck to process it.