Angel Lopez-Sanchez: Multiwavelength galaxy studies

There are way too many good talks around here that I don’t post about for lack of time and organization. I’ve been revamping my lifestyle in several ways lately, and have made more or less inviolate time for exercise and calling home, so blogging can’t be far behind — it’s just a matter of figuring out where to put it.

We had two RSAA colloquia this week, both of which were excellent, and both of which were out of my field of expertise. It’s such great validation to go to a really good talk that’s not about what you do all day — even if you only learn a few things, it’s more than what you knew before. Generally I learn more either from reading or doing than from listening, but there are definitely exceptions.

One of these talks, given by Jamie Lloyd of Cornell University, talked about the evolution of stars with exoplanets. There was lots of great scientific content, but the most interesting thing I learned there, in case I don’t have time to write about it later, is that there’s an open-source stellar evolution code called MESA. It’s maintained by Bill Paxton, one of the founders of Adobe Systems who’s turned to astrophysics in his “retirement”. Apparently it’s quite good, so if you have a computational bent and are interested in the lives of stars, go play with it!

The other was given this morning by Angel Lopez-Sanchez of the Australian Astronomical Observatory, about the multiwavelength appearance of galaxies. Normally I’m not a galaxy kind of guy, but he’s another local postdoc and I wouldn’t feel right if I didn’t support him. I hadn’t heard a really good galaxy talk since John Kormendy came through last fall to tell us all about galaxy evolution — I still have notes from those talks (plural), which I should post. So I figured I’d listen in.

First of all, the talk was visually stunning in ways I didn’t expect. Back in grad school I used to work on blazars, so when I hear the word “multiwavelength”, I usually think of it in the context of processes that form jets in AGN, so “multiwavelength” here means gamma-rays, X-rays, radio, and optical. There are a bunch of plots showing that to pin down how particles are accelerated to high energies, you need access to all these wavelengths. The relevant visuals are usually spectral energy distributions SEDs which look like the ones shown on this page from my old friends at Yale — interesting, but hard to get really excited about unless you work on these objects specifically.

Angel’s images combined ultraviolet (young stars), optical (ionized gas), near-infrared (old-stars), mid-infrared (dust) and 21-cm radio emission (from the 1.4 GHz spin-flip transition in neutral hydrogen, or H I). You can see some examples here that look like the ones he showed us. Seeing how different wavelengths can separate the different components of what the galaxy’s made of is pretty darn cool. I didn’t catch the majority of his words, but I think the pictures showed most of what you really needed to know. Here’s an example inline for those who can’t be bothered to click:

The H I imaging was probably the most surprising thing — try mousing over the version of the image under the link. It shows that the neutral gas content of these galaxies is way more spatially extended than the stars are, sometimes three or four times bigger than the optical part of the galaxies. The question naturally arises: where does all this gas come from? Has it always been associated with the galaxy, or did it fall in from other galaxies or from elsewhere? I heard it suggested recently in another talk that one explanation for the disks of spiral galaxies is that gas falls in from outside and falls in the disk, keeping a torque applied so the disk spins up and spreads out.

I think the jury’s still out on that question, but it appears to be a key science question Angel and his colleagues want to investigate when they get the chance. There’s a lot of cool new radio hardware coming online in the next few years, which will get the chance to make images like these for hundreds of nearby galaxies and their surroundings. It would be even more interesting to compare high-redshift galaxies with low-redshift ones, or track the H I spatial extent as a function of redshift and environment, so you could see the gas get sucked in…


About Richard

I'm an American scientist who is building a new life in Australia. This space will contain words about science and math, but also philosophy, policy, literature, my travels, occasional rants, all sorts of things I find strange and awesome. The views expressed in this blog do not necessarily reflect the opinions of my employer at the time (currently University of Sydney), though personally, I think they should.
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