More Outliers from the Mass–Metallicity Relation

Last week, my second paper on outliers from the mass–metallicity relation showed up on astro-ph. In the first one, which I described here, was on the low-mass high-metallicity outliers from the relation; I described in that first post more about what this so-called "mass–metallicity relation" thing actually is. We concluded in that paper that those galaxies must be running out of star-forming gas, and thus nearing the end of their star formation.

In Paper II, we are looking at the other corner of the mass–metallicity plane: massive low-metallicity galaxies. (Yes, it is easy to get tongue-tied in this game.) Most of the 42 galaxies in our sample look like this:They are very blue and what we astronomers called "disturbed." That's fancy-talk for "they've been playing rough with their neighbors and so their gas and stars have been all moved around so they look morphologically... disturbed." The key here is that simulations have shown that as galaxies interact, gas from really large scales will typically get drained into the centers of the galaxies. As it turns out, this large-scale gas will generically have a much lower metallicity than the gas originally at the galaxy center, so the large-scale gas inflow will effectively dilute the central gas. Relative to the amount of time we can expect for the star-formation to continue, it won't take very long for this new gas to get re-enriched by metals formed during the star formation itself, so we can expect for these luminous low-metallicity galaxies to be relatively rare.

Book Review: Coming of Age in the Milky Way by Timothy Ferris

(Two posts in less than a week. I know. Don't get too excited.)

I recently finished reading Timothy Ferris's Coming of Age in the Milky Way. I admit: it was on a recommendation list somewhere and I was intrigued by the title, so when I saw it at a local used bookstore, I snagged it. I have not been disappointed.

Summary: Coming of Age in the Milky Way tells the story of how humankind came to know its place in the universe. Though the book has three distinct themes (Space, Time, and Creation), the main focus is on Space: how did we learn the size of the Earth, the extent of and laws governing the Solar System, that the Milky Way is a "galaxy" and only one of many, and that the universe is giant and expanding? The other two sections expand on this history of revelations. The Time section discusses how we discovered that the Earth (as well as humans as a species and the universe as a whole) are not unchanging, static and infinite, and the Creation section focuses more on the marriage of quantum physics and cosmology: how did the elements and subatomic particles and, indeed, the universe itself come to be?

Review: As an astronomer, none of the actual science here was new to me, but I can say that, unlike many popular treatments of physics, very little of the descriptions made my inner "but that's not really true ..." voice cringe. (There were maybe two pages like this, and one of them may have actually involved something that was believed to be true in the late 1980s.)

Primarily, though, this is a history book, and I found the history fascinating. Ferris paints a detailed and colorful portait of the personalities and worldly changes (politics, well-timed supernovae, etc.) that led to these revelations (and occasional setbacks). The writing is lyrical, poetic even, and yet detailed and straightforward when need be. The book is stock full of quotes, none of which feel out of place or difficult to read (as thousand-year-old quotations are apt to be). The transition of this writing style into the modern age—when quotes were garnered via interviews instead of meticulous combing of however-the-hell people figure these things out—was seemless. Though published in 1988, Coming of Age in the Milky Way is surprisingly not out-of-date 20 years later; as the views of the 1980s are not treated as The Answer, a 21st century reader will only notice that the story seems to stop a little earlier than expected.

I thoroughly enjoyed this book, and I recommend it to anyone interested in the history of science, the process of science, or general astronomy or physics.

Paper Summary: Metal-Rich Dwarf Galaxies

Towards the last week of January, when I was hugely absorbed in trying to figure out a thesis proposal thing, a professor came into my office and started talking about the mass–metallicity relation. I knew about it, of course, but here was a new, simple idea: are the extreme outliers from this locus of galaxies real? In the spirit of a short "one month" project, it's now about three months later, and we've "finally" got a paper on said outliers on astro-ph. (I think this is a great example of: if anyone ever offers you a great idea, take it and run with it.)

So to back up a bit. What's this "mass–metallicity relation"? The short version is that a correlation exists between galaxy mass and metallicity such that the more massive a galaxy is, the more likely it is to be "metal rich." Originally this was the luminosity–metallicity relation, since how bright a galaxy is is much easier to measure than how massive it is, so on the right here I've plotted metallicity versus "absolute magnitude" in small grey points for a large sample of star-forming galaxies (remember: magnitudes are silly, so the right-hand side is brighter than the left-hand side, even though the numbers don't increase in that direction). Our outliers are, well, the larger red and green outliers from this relation; the different colors simply denote slightly different ways of selecting different subsamples. Astronomers being astronomers and not material scientists, when we say "metals" what we really mean is "any element which could not have been made in the Big Bang, i.e., basically anything not Hydrogen or Helium (or maybe Lithium but there's so little of that we'll completely ignore it)." There is of course a nice slew of caveats. The first is that the easiest way to measure the metallicity of galaxies is to limit ourselves to star-forming galaxies; all of those nice new young stars heat up the gas around them, and then as this gas cools it gives off emission lines. We can then look at the spectra of these galaxies and by measuring the how how strong various lines are relative to one another and combining it with some black magic (a.k.a. "spectral synthesis codes") we can measure the ratio of oxygen to hydrogen in a star-forming galaxy's gas. So I (and others!) basically use "metallicity" and "oxygen abundance" interchangeably, and, more precisely, I basically always mean "gas phase" abundance.

One of the interesting interchanges between theory and observation is that sometimes there will be some interesting observation (such as the obervation that galaxy mass and metallicity are correlated). So theorists will come up with a bunch of reasons why this is the case, and a few will even attempt to give explanations fo the scatter about the observed relation. A robust theory will also be able to explain seemingly strange galaxies: if a theory is able to explain why low mass galaxies have such low metallicities, then it should also be able to predict in what ways a low mass galaxy with high metallicity is different from its more mundane cousins. I spend a lot of the paper exploring various explanations (and then eliminating them) for why these galaxies could be so "weird," but I eventually hit upon one explanation which, in retrospect, is blindingly obvious.

The idea is that low mass galaxies have low metal abundances because they have low star formation rates and relatively high gas fractions (i.e., the fraction of their mass that is in gas rather than stars is large). An easy way to think of this is like so: stars turn hydrogen and helium into more massive elements (metals). As stars are formed, they the most massive ones die quickly, throwing their metal-rich selves back into the surrounding gas, thereby raising the metallicity of that gas. But a low star formation rate in a high gas fraction environment will not be making enough metals in order to fully pollute the gas around it, and so the fraction of metals in the gas will be relatively low. (This argument only really works for low-mass galaxies, but since those are the ones we're interested in, I'll ignore that subtlety for now.)

So how do you get high-metallicity low-mass galaxies? Well, presumably the galaxy would need either a very high star formation rate (so the massive stars can actually pollute the gas) or a very low gas fraction (so each supernova has a higher impact on the gas). We find that these outliers don't have unusually high star formation rates, so we conclude that they must have rather low gas fractions. But this is the same gas the stars are forming out of! So the star formation must not have very long left to go. A nice bit of supporting evidence for this scenario is the occasional mention in the literature that so-called "transition" dwarf galaxies tend to have low gas masses and higher-than-expected gas-phase metallicities; these galaxies are known as "transition" objects because they are between regular star-forming dwarfs and quiescent non-starforming dwarf galaxies. The especially neat part is that several of these galaxies have the star formation limited to their centers (like this galaxy to the left: blue in a galaxy is a sign of lots of young, recently formed stars). One way to interpret this is that star formation used to occur on all scales in this galaxy, but the gas has since been extinguished (or blown out of the galaxy) at the larger scales.

Another Peanut Star: This One's Yellow!

This was actually discovered a few months ago, but now there's a press release and even a movie: a peanut-shaped binary star system has been discovered (with the LBT!) in the dwarf galaxy Holmberg IX, a companion to the beautiful spiral galaxy, M81:

And, yes, despite the unfortunate date chosen for the press release, this is a real star, and it is actually exciting. And I take full credit for the term "peanut star." Just please ignore the fact that the movie makes the stars look like they're being externally illuminated instead of, you know, generating their own light.

Solar System Analog Revealed by Microlensing

Normally I don't blog about astronomy in the news, usually because it's either boring or poorly spun or everyone else has already done a more thorough job of it than I'd be willing to anyhow. So I'm stunned that even though it was announced three days ago, I have seen no mention on my portion of the blogosphere about the first discovery of a solar system analog—even the Bad Astronomer only mentioned the independently discovered and announced merely Jupiter analog, though the solar system analog is arguably a much bigger deal since it has both roughly Jupiter and Saturn mass planets.

So how was this system found, why is it important—and why do I suddenly care about planets? The last question is easy: the lead author on the paper is Scott Gaudi, a professor here at Ohio State, and in fact much of the modelling and work that went into deciphering the event's lighcurve was done by one of my officemates. I say "event" because these ~0.7 and ~0.3 Jupiter mass planets around a roughly half solar mass star were found via gravitational microlensing; the star system happened to pass immediately in front of another star relative to Earth, thus magnifying the background star. The change in apparent brightness of this background star is affected by how the mass in the lensing star system is arranged, and so a detailed analysis of the lightcurve can reveal planets in the system. (If you want real details, I think the press release does a fairly good job.) What is so exciting about this particular event is that this is the first time there has been a bright enough microlensing event that has been followed closely enough to be sensitive to a Jupiter+Saturn planetary arrangement—which strongly suggests that such systems (such as our own!) are extremely common.

UPDATE (02/19/2008): Apparently I didn't do a very good job explaining why this is exciting. An astronomer asked me:

I'll grant that it's interesting, but is it really unexpected? The first extrasolar planet discovered was potentially exciting. Now, hundreds are known, and it's clear that their discovery is limited only by the amount of time and money devoted to finding them. Extrasolar multiple-planet systems are also known. Or to put it another way, I'd perhaps be more shocked if a Jupiter-Saturn analogue hadn't been discovered after a little more than a decade of finding massive extrasolar planets.

My reply: Surprising depends on who you ask, but while there have been plenty of exoplanets found (and maybe 2 dozen systems with multiple planets), most of them have been close-in planets, so-called "hot Jupiters" ... planets with periods of only a few days, maybe up to several tens of days. Radial velocity studies have only been going on for about ten years now, which is why they are just now (as in, last week) announcing planets in roughly 10-year orbits: they are restricted to monitoring nearly full orbits to be sure what they are detecting is a planet. Microlensing is the only planet-finding techinque that is actually more sensitive to far-out planets than close-in ones (both the radial velocity and the transitting signal are higher for close-in planets), but people haven't been using it to look look for planets as extensively and as long as they have RV and transits. So it is more comforting than "surprising" that we have found a solar system analog: for years the only systems found were crazy things that looked nothing like our own solar system.

Awesome

This paper by Conroy, Wechsler, and Kravtsov has got to have the best footnote I have ever seen. They put forth a straightforward way to model "galaxy clustering through cosmic time," and their model does a surprisingly good job of mathing the data. The text to sum this all up reads: "Overall the agreement is excellent on all scales for all four samples.⁸"

Footnote reads: "⁸ Booyah!"

Hotel Mauna Kea

What is it like to observe on Mauna Kea, the tallest mountain in Hawaii? Hat tip to the Angry Astronomer:

More astro-ph Nuggets

Today's first piece of fun on astro-ph is a short paper by Travis Metcalfe on "The Production Rate and Employment of Ph.D. Astronomers," or: how difficult is it to get a tenure-track job given that you have a Ph.D. in astornomy? I haven't actually read this preprint, but Travis had a very interesting poster at the AAS meeting last May on the same topic, so I am guessing it is based on the same information.

The second is a short conference proceedings by Chris Stubbs on the Crisis in Fundamental Physics, or, what will happen if w really does equal -1. Translation: what if the properties of the dark energy really are the most boring vanilla stuff we can come up with ... and thus also boring both theoretically and observationally. This, combined with Simon White's screed from a few months ago, paint the question of dark energy as inherently interesting (there is something going on in the universe that we really don't understand, and it might be related to why our really-good-for-everything-else theories of quantum mechanics and gravity don't play nice together), but in the meantime it poses a scientifically and sociologically potentially crippling/stagnating problem.

How to Measure the Masses of Galaxy Clusters

I've spent some time recently thinking about the usefulness of galaxy clusters in astronomy and cosmology (aside from them being interesting in their own right). As the most easily identified most massive structures in the universe, one obvious parameter that is often desired of them is their mass. But how does one go about weighing the most massive objects in the universe?

Stellar light: This is the simplest and most straightforward way to measure the mass of a cluster, but it also requires the most assumptions. The basic idea is that if you know how much light the stars in the cluster are emitting, and if you have some good guess at how much mass a cluster of a given luminosity is (i.e., the "mass to light ratio"), then you can estimate the cluster's mass. An even simpler version is to just count up the number of galaxies in the cluster, and say, "well, clusters with this many galaxies have on average about this mass ..." And, counting the number of galaxies in a cluster is actually rather trickier than it sounds because it takes a lot of telescope time to verify that individual galaxies are in fact cluster members.

Galaxy velocity dispersion (also stellar light): If you're going to go through all the trouble of verifying which galaxies are actually in the cluster, then you can actually measure the mass of the cluster rather than merely estimating it. By taking the velocity dispersion of the galaxies along the line of sight, and assuming that the cluster is relaxed and in virial equilibrium, you can measure the mass, which is essentially proportional to the square of the velocity dispersion.

X-rays: Galaxy clusters have a lot of hot ionized gas in them. This hot gas emits high energy photons due to what is known as "bremsstrahlung": when an electron changes course as it goes whizzing past a (positively charged) ion, it is accelerating, and therefore gives of radiation. We can measure the temperature of the gas from this radiation, and like with the galaxy velocity dispersion, when we assume the cluster is in virial equilibrium—not always an accurate assumption, especially if, say, the cluster is merging with another cluster, or just forming—then we can calculate the mass of the cluster. This is one of the most popular and straightforward way of measuring cluster masses; the only tricky part really is the fact that one has to go to space in order to get X-ray data.

Weak lensing: As light from galaxies passes near a cluster, the cluster's gravity causes the light's path to bend slightly, which in turn causes the shape of galaxies behind the cluster along our line of sight to appear slightly disorted on the sky. (If you want a less hand-wavey explanation, you can look at this post I wrote last year. The mass and the physics are the same, even if the regimes are slightly different.) By measuring the average shape change of background galaxies in different annuli around the cluster, we can measure the surface mass profile of the cluster. Many people will argue (including me, perhaps) that weak lensing is the only way of measuring the entire cluster mass—gravity only cares about where the mass is, not what is causing it, and so gravitational lensing is sensitive to the underlying dark matter profile of the cluster, not just where the gas, galaxies, or light happen to live. Weak lensing is also a nice technique because it can be done with ground-based telescopes using visible-wavelength (or near infrared) light, but it does not require a plethora of spectra like galaxie velocity dispersion measurements do. Converting a measured weak lensing profile to an actual cluster mass estimate, however, involves converting a surface mass density excess to a surface mass density (i.e., the "background" surface mass density must be well-estimated) and then converting the surface mass density to a mass (i.e., assumptions about the three-dimensional structure of the cluster must be made in order to turn a two-dimensional map into a three-dimensional mass).

Sunyaev-Zel'dovich effect: One of the most exciting and promising new ways of measuring cluster masses is through their imprint on the cosmic microwave background (CMB, or as "real cosmologists" call it, the "camb"). As a CMB photon goes through a cluster, it will interact with some of the high energy electrons in the cluster's hot gas (the same ones responsible for the X-ray emission). The result is that the CMB photon gains a little bit of energy, causing the CMB to appear hotter in the direction of the cluster than it would be in the cluster's absence. Through a conspiracy of math and physics, the change in CMB intensity is essentially due to the cluster's mass alone—and because the clusters are relatively close by compared to the surface of last scattering (the origin of the CMB photons), the SZ signal is basically independent of the cluster's redshift. The redshift independence is both a blessing and a curse: while we can theoretically detect high-redshift clusters with the SZ effect, we have no way of constraining their redshift using the SZ effect alone—and high redshift objects are exactly the ones which are more difficult to detect and study using the other techniques I've described here. The SZ effect has been observed for several clusters, but to date no clusters have been conclusively discovered from their SZ signature. This may change soon, however, as two telescopes (the South Pole Telescope and the Atacama Telscope) capable of detecting the SZ effect have come online in the past year. At the very least, the SZ effect promises to be a powerful technique for constraining the measurements from the other techniques described here.

Astronomers Stuck in a Cloud

I've been at the MDM observatory near Tucson since yesterday around sundown, and last night I started a blog post which looked something like this:

Well, I'm back on the mountain, and it is raining. A lot.

And then the power went out, and since the generator was down as well, we had no power, no heat, no internet, and—after a few hours—no phone either. We were in the middle of a cloud, a white windy rainy mass, wherein we had no connection to the outside world. It's an odd thing, being in a dark building with only a couple of flashlights in the middle of storm after everyone else has gone to sleep, and I (having been staying up late in this time zone for several days already) was the only one awake. So I sat around for a while thinking about galaxies and stars and clusters how everything is interrelated and how I'll never come up with a thesis topic.

Today has been more lighthearted—and more of an extended hurricane party, but with more astronomy and rampant silliness. The first year grad students are here this weekend, nominally to learn how to observe. (Does learning how to do a lightning shutdown count?) They have finals next week and so there has been a lot of questions buzzing around along the lines of "Why are metal poor stars bluer and fainter than metal rich stars?" and "What's the difference between the Tully-Fisher relation and the Fundamental Plane?" Between this and the conference last week (more on that later), I feel as though I've been walking in an astronomy-saturated fog for a week.

The power came back around 2:30pm and the internet and phone followed around 4. With the return of the outside world, there has been a lot of online Scrabble (yes, I've been converted) and now the watching of the Oklahoma-Missouri game on the small TV in the kitchen ... something about if Oklahoma wins then it is good for Ohio State and if Ohio State wins the national championship then alumni will want to give more money which will eventually be good for the astronomy department.

Science and UnScience

I'm headed to Tucson, AZ today for an astronomy-laden week, complete with a conference and some observing (weather permitting). Among my flight reading material is an essay Edwin Salpeter (yes, as in, the Salpeter IMF [initial mass function]) posted to astro-ph last week with some interesting anecdotes and observations on astronomy pre-1957. On the other hand, if you're looking for something less informative, but perhaps more flavorful, you can read any one of the numerous screeds on the recent hogwash in the New York Times about science really actually being faith in disguise (which, by the way, it's uhm not).

Science: Still Awesome

Just in case you were wondering, science is still awesome.

First up, synesthesia—the mixing of senses so that, for example, one associates or experiences certain colors with individual numbers and letters—is always cool. I have this to enough of an extent that I would totally love to have it even more. For example, in my mind Thursdays are a deep mustard color, but Tuesdays are a rich green and Wednesdays are a pale blue; I wouldn't be surprised if this association is one reason why I don't have to keep a calendar or datebook. The recent incredibly wonderful thing I've found out about synesthesia is that apparently colorblind synesthetes can experience colors via associations that their eyes are not actually capable of seeing. Brains are so fantastic.

I've been taking art classes at the local cultural arts center since June. Over the summer I took a clay sculpture class, and when I went back on my second week to look at what I had started, I was rather freaked to discover that the piece was partially covered in mold. Turns out, the more microorganisms there are living in clay, the more aerated the clay is, and thus the higher quality it has the potential to be for sculpting. Also in the art department, last week I was working with two pieces of sheet metal (I'm taking a jewelry class now) that I wanted to have have identical borders, so I superglued the two pieces together so they wouldn't move relative to one another as I filed the edges. But then I wanted to, you know, unsuperglue them. The most efficient way to do this, apparently, is to simply anneal the metal—that is, put it under a big torch until the superglue burns away and the pieces come apart. I was working with copper, which normally when annealed turns a nice deep red color, but with the superglue on it, turned a dark grody grey.

It's been all over the news, and I obviously didn't get around to writing this post yesterday, but the Auger collaboration has finally come out with their first big result: cosmic rays appear to not be isotropically distributed on the sky. They come just short of saying that comsic rays are produced by supermassive black holes (specifically, supermassive black holes actively accreting matter), but due to a liberal use of the subjunctive in the paper, this is essentially the take-home message. Chad has already done a detailed analysis of the paper and all that jazz, but he fails to mention the fact that the effective size of the Auger detector, located in Argentina, is roughly the same area as Rhode Island—and they're looking to expand. I'm not sure if this is just a statement of how large their detector is, or how small Rhode Island is, though.

δ Carina: A Narrative

So the new kitty's name is now officially δ Carina. You may call her δ, Carina, or Carrie for short, but she probably won't respond to any of them. The choice of δ Carina as a name, in retrospect, was incredibly obvious. I had originally been trying to decide between Cassiopeia and Carina (and so either Cassia or Carrie for short), but for such a hyper little hairball, Cassiopeia seems a little to sophisticated. So Carina it is, but the all-too-obvious nickname/association with Carina is Eta Carina, the stupidly massive old cranky variable star in the constellation Carina. And my little bundle of skittish cord-chewing energy is neither massive nor old enough to be an η Carina, so the obvious other choice was Epsilon Carina (since in the land of mathematics ε is generally small but nonzero quantity). But as it turns out, eps Car is a binary star, and since I've got one cat and not two (though, seriously, ε Carina A and ε Carina B would be awesome names for sibling kitties), that was Right Out. So, in the spirit of taking the limit of small delta and epsilon-delta balls, δ Carina became the new name nominee; the only remaining question was: what kind of star is δ Car?

Well, as it turns out, there is no star δ Carina. The Bayer designation of stars names stars in a constellation as Alpha, Beta, Gamma, Delta, etc. from brightest to, er, less bright; so, for instance, Alpha Centauri is the brightest star in the Centaurus constellation. So how can a consellation have no fourth brightest (i.e., Delta) star? Glad you asked. See, back in the day, Ptolemy made a list of the 48 constellations in the sky. One of the largest was Argo Navis, the Southern Ship. So there was an Alpha Argo Navis, a Beta Argo Navis, etc. But when the constellation got broken up in 1752 into Vela (the sail), Carina (the keel), and Puppis (the poop deck [hehe]), astronomers, being astronomrs and thus logical in all ways, decided to also split up the stars and keep the Greek lettering instead of, you know, re-assigning the names to the actual nth brightest stars in each new constellation. So, α and β went to Carina, but γ and δ are in Vela—leaving the name δ Carina free to be assigned to my new 9-week-old clingy attacking striped meowing fuzzball.

And so, as she attacks my hands and legs and arms and keyboard and oh my god I hope she's going to get tired out so I can get some sleep tonight, I present to you δ Carina, The First Day: A Narrative.


Oh no!! A new place! What do I do? I'm all trembling and scared.
Cords! And a ball! How do I choose??
Shoes!!!! My favorites! How did you know??
OK time to read some but how do I choose?
That was lots of hard work now it's naptime.
Whoa. I fell off that was scary. I'll hide here and let Athena the Raccoon protect me.

Clouds, Clouds and More Clouds

I'm in the middle of a six night observing run at the MDM 2.4m telescope on Kitt Peak near Tucson, Arizona. This evening threatening clouds at sundown turned into enough lightning at the horizon to do a lightning shutdown—that is to say, after not bothering to open the dome and try to look at anything, I had the pleasure of shutting down the half dozen computers that run the telescope and its instruments, etc. as well as their UPS backup power supply. I've heard plenty of talk before of how annoying it is to be an astronomer on a cloud-covered mountain, but I always thought the irritation arose mainly from the lack of ability to take data, when in reality it's more like an irritation arising from the lack of anything to do. The last few nights have been cloudy off and on, but mostly with the patchy kinds of clouds that tease you as you chase for holes between them, or like last night when everything was beautiful and clear and we were efficiently going from one target to the next until around 1a.m. when in less than fifteen minutes the humidity rose by 10% and the sky became a thick blanket of white and we had to close up for the remainder of the night.

The run I am on is for "queue observing." The basic idea behind queue observing is that if a bunch of people have objects they'd like to have looked at once a night for a period of time, then they can combine resources and take turns observing all of the objects. In this case, "resources" are "graduate students who feel like getting some observing experience and perhaps their names on a paper or two." The main part of this queue observing run is to take spectra of supernovae for SDSS. SDSS is good enough at finding supernovae that, while they're looking (i.e., in the fall) there is always a list of supernovae to observe, and, unlike other kinds of transient objects (like gamma ray bursts), supernovae are generally bright for about two weeks.

This 2.4m telescope is, I believe, the largest in the world that does not have a regular night operator. That is, larger telescopes have a staff of people whose job it is to actually run the telescope: they open the dome and turn on the instruments and take the calibration images and make sure the telescope is pointed in the correct direction with high enough precision and is nicely focused and that everything is working nicely. Not so here. Here it's just me (well, there was another graduate student here the last three nights, but no staff at night), and so when it's actually safe to, you know, turn on the telescope, then I get to make sure that all of those things happen. The first night or two is usually hell because there are so many things to remember and it takes a while to completely nightshift and get used to the higher altitude and lower humidity; tonight is hell because there isn't anything to do and I didn't get up until 4pm so it's not like I can "just go to sleep."

Well, actually I did bring some DVDs from Netflix with me. I've already watched a disc of Lost and Buffy the Vampire Slayer (I've only recently started watching both shows). Seriously, all alone in the dark on an empty quiet mountain... I'm now surprisingly jumpy. And I'm not liking the forecast of it not clearing up until Tuesday night.

Google Sky and Astronomy for the Masses

So some lady just called me looking for the Political Science department .... I told her that I am in the Astronomy department, not Political Science. So she asked me if I believe the universe is expanding. Yes ... "That's because of the redshifts, right?" Yeah ... "So who owns the Hubble telescope?" Uh ... "The US Government owns the Hubble telescope, right?" Well, I wouldn't put it quite like that. "The French government doesn't operate it, so it must be the US." Does that really follow? "Astronomy is a science, right? What's the phone number of the chair of the science department?" Uhm ... It's 6pm... I don't think anyone is going to be in their offices right now.

Sigh. I clearly need more practice talking to crazy people while still allowing them to remain "interested" in astronomy, though this one seemed rather well-informed, albeit with big warning bells going off all over the place. In other news, Google announced today that the Sky is now part of the Earth, in that Google Sky is now part of Google Earth. This was enough of an incentive for me to finally download Google Earth and waste lots of time looking at pretty galaxies and galaxy clusters and nebulae and other such fun things. Constellations and planet orbits are included. Much like Google Earth, Google Sky is much more in the hokey fun category than the useful category, and unfortunately the objects I'm prone to looking at first are the ones I know well enough to be annoyed at how poor some of the data is. The entire sky has been mapped by the Digital Sky Survey (DSS), and a fourth of it by the more recent and absolutely fantastic Sloan Digital Sky Survey (SDSS). The Sloan images include all of the delightful astrometric precision of SDSS, as well as all five wavelength bands of the survey. Then, for the popular select few objects, the Hubble Heritage project has kicked in with "informative" blurbs about "zoom lenses" (also known as "the Virgo Cluster") and other such things, though one useful bit about these is the links to outside sources like ADS for said objects. The Hubble Heritage project by itself is a pretty interesting archive to nose around in if you haven't already, as well as the recently released Hubble Legacy Archive (which is actually good for scientific purposes).

Galaxies!! Part Two

Waaaaay back in June—as in, last June—I wrote a long post explaining the background, mostly about galaxies, needed to understand the work I've done on the connection between how strongly barred a galaxy is and what kind of structure its circumnuclear dust takes on. (If you want to understand the results below, I recommend reading the background post first. Also, the poster for the conference I presented this at last year can be found here.) The paper was published on December 1, and it is this paper that I will be presenting next week for the oral portion of my general exam, so I figure it's about time I get around to explaining to y'all some of the actual, you know, results.

The first step in preparing next week's talk was to re-read this paper I haven't touched in nearly a year. This has been fun, not only for the "wow! galaxies are cool!" aspect, but also because I can think things like, " 'Employ'? We employ this technique? Didn't we really just use it??" Also, all of those figures I thought were gorgeous a year ago? Turns out the font is too small on most of them, and at least one of them has a typo (as well as one table).

Our first main result was that tightly wound nuclear dust spirals are primarily found in galaxies lacking bars. This isn't all that surprising due to boundary conditions: for the dust in a circumnuclear spiral to connect to the (radial) dust lanes in a bar, the spiral must unwind somewhat, and tightly wound spirals are not somewhat unwound.

So what kinds of circumnuclear morphologies do strongly barred galaxies take on? One common feature is what we term "large grand design" (LGD) spiral structure. A LGD spiral has two prominent symmetric spiral arms which, in 90% of our LGD galaxies, distintegrate before reaching the galaxy nucleus. One frequent end for these spiral arms is at a circumnuclear starburst ring. A circumnuclear starburst ring is just what it sounds like: a ring of intense star formation and thick dust surrounding the galaxy nucleus, like the example to the right. Here, the LGD structure are the dark dust lanes on the top left and bottom right of the image, which connect onto the ring itself. Inside the ring, we see a loosely wound nuclear spiral which is distinct from the ring itself, and is likely to be "native" dust; that is, the bar is probably ineffective at funneling material to the very center of this galaxy. In our most strongly barred galaxies, those lacking LGD spirals simply have very chaotic centers (at best, a chaotic spiral), potentially with a lot of ongoing star formation.

Day 3 at the 210th AAS: I Am So Tired

Yesterday was a slow day for me. While there were several individual talks I was interested in going to, there weren't any sessions I was willing to stay in for more than half an hour. But since yesterday was the first day my poster was up, I spent most of my time hanging out in the poster room. The two posters on either side of me were getting a lot more traffic. One was simply an interesting idea involving the gravitational lensing of gamma ray bursts by primordial black holes as will be viewed by GLAST; instead of a "classical" lensing, an interference pattern should be seen in the signal. While the probability of such an event is low (10^-5) and contingent on which model of primordial black holes and subsequent destruction you take, it is still a neat idea. On the other side of me was a poster about the dynamical origins of the local Hercules stream—they think it's due to a dynamical ripple thanks to the Galactic bar. People like hearing about the structure of the Milky Way, so this project was one of the three discussed at the press conference I attended (as an interested listener) in the late morning.

In the afternoon, also in the exhibit hall, I got the chance to go inside the Star Lab they have set up in the corner of the hall. For the low low price of $15,000 you too can own the ultimate tent for camping out in the living room. The Star Lab is essentially a portable planeterium, a big grey plastic bubble that you crawl into, with the stars projected onto the inside surface. The inside of the bubble goes up to 10 feet high and is large enough to lay down in while the presentation is being given. The presentation I was given focused on Hawaiian navigation: how did the Polynesians and Micronesians find Hawai'i? Apparently there was this big controversy about four decades ago over whether or not the Hawaiian islands were "stumbled upon" or purposely found. I don't really understand how you can purposely go find something you do not know (or have reason to believe) exists, but anyhow. In the 1970s a group called the Polynesian Voyaging Society formed themselves and learned how to navigate cross-ocean using no instrumentation. They built a few double-hulled canoes and went from Hawai'i to Tahiti... with no instrumentation. In canoes. We re-learned all of the familiar constellations and asterisms with their Hawaiian legends, and a few of the more southern constellations I have never seen with my own eyes.

Today is the last day of the conference, and things will be pretty much done by lunchtime. I have no idea of details yet, but I'm hoping to find some people to explore the island with... I've gotten only a few blocks from the hotel and convention center since arriving here on Sunday.

Day 2 at the 210th AAS: Wide Field Surveys

Yesterday there were no big invited talks, only posters still up from Monday and three day long topical sessions: Astrophysical Ionizing Radiation Sources and their Impact on Life (think about how nearby supernovae or the orbit of the Sun around the Galaxy might have affected evolution type thing), Turbulence in Diffuse Astrophysical Environments (the majority of the talks here had "turbulence" in the title), and Wide-field Surveys in the 21st Century. I spent the day in the Wide-field Surveys room, and I got to hear a lot about how Pan-STARRS is going to be amazing, but in general I liked most of the talks because I like it when astronomy can be a "real" statistical science instead of mere stamp collecting. The two main reasons, I think, why people keep talking about Pan-STARSS here is because it's starting this year and because it is largely based in Hawaii. (In the afternoon I finally heard why I had gotten the impression that people outside of the Pan-STARRS collaboration speak of it with a bit of a sardonic or deriding tone in their voice; apparently it got its funding as a rider on some bill in Congress... was it the Iraq war bill?)

Lunch yesterday was the calmest of my meals here; I went out with just one of my officemates who is here, a former grad student from Ohio State who is now planet hunting at Space Telescope Institute (and actually finding them, unlike when he did his thesis), and another guy from STScI. It's been less true even this meeting than when I attended the 2005 winter meeting of the AAS in San Diego, but one of the nice things about these kinds of meetings is seeing people you haven't seen in a long time. I've been meeting a lot of new people, certainly, and as I guessed before coming, attendance here seems to be dominated by grad students and young postdocs.

Today will be much more interesting: my poster goes up today and I'll be attending a press conference, so stay tuned for tomorrow's report!

Day 1 at the 210th AAS

To the left is the view from my room. It is sunnier this morning, but yesterday I enjoyed watching the fog (or perhaps that is rain?) in the valley lift up and re-descend. Jet lag here isn't so bad; I like the concept of being a morning person, but in practice it never holds.

The conference kicked off yesterday morning with a talk by John Tonry on Synoptic Sky Surveys. Essentially, the Sloan Digitial Sky Survey (SDSS) is coming to a close. Sloan has mapped about a fifth of the sky in visible wavelengths, with stupidly large numbers of cataloged stars, galaxies, quasars, and what-have-yous. I think in some ways the holy grail of observational astronomy is to have the entire sky mapped down to the faintest magnitudes possible, at all wavelengths, and to continually observe the entire sky for time variability. According to Tonry, we are rapidly approaching the first goal for visible wavelengths; it is likely that in ten to twenty years, the entire optical sky will be mapped down to the faintest magnitude allowed by the atmosphere. Surveys like Pan-STARRS and SkyMapper are coming online this year. In 15 years, will astronomy be a field of searching databases and waving the wand of statistics, or are we practically already there with SDSS?

After the first talk, everyone trickled down to the room with the posters and exhibits; more specifically, the room with the pastries and coffee. I like going around to the exhibits and talking to the people there; I've already collected half a dozen bookmarks (to make up for forgetting to bring one with me) and more stickers than I know what to do with.

Then it was time to break into individual sessions, with five minute "normal" talks and fifteen minute "disseratation" talks. Several people simply did not show up to give their talk in a few of the sessions I attended; I cannot understand how someone can not only just not "show up," but also be rude enough to not inform the organizers that their plans have changed. I managed to miss most of the talks I had wanted to go to, since I was skipping around the galaxy evolution and galaxy cluster and variable star sessions, but most of the talks I heard were in fact interesting.

At lunch, I found myself with a solar physics group from Boulder, Colorado. This meeting is in conjunction with the Solar Physics Division, which is to say, there are a lot of astronomers here who have taken the "day shift." The sun is fascinating; one would think that being the nearest star, we would know everything about it we might want to. But people don't even agree on simple-seeming things, like the amount of oxygen relative to hydrogen. It is also an interesting field in that we can measure all sorts of things from the sun that we can't in other stars: details of sunspots, coronal mass ejections, granulation, helioseismology, sun flares, etc. etc.—things we would looooove to know about Other Stars, but we just can't make the measurements yet. After all, the sun is just a star, and what we really want to know about is stars, and in many plots, we only have the one data point. A few of the solar folks I talked to are excited about the upcoming missions to search for extrasolar planets; by making exquisitely accurate measurments of the light coming from stars, we can also hope to learn about astroseismology (literally, starquakes) of stars not our own.

Speaking of extrasolar planets, apparently the big news release yesterday was on a bunch of new ones being announced. (One of the breakout sessions yesterday was on extrasolar planets, but I did not go.) There have been rumors circulating for months that 2007 will see a huge increase in the number of known extrasolar planets; many of the ongoing searches for transiting planets are finally coming to fruition. It is heartening to see people announcing more than a handful of planets at a time; it means that the field is growing from one of stamp collecting to one in which they can actually do statistics and begin to really learn about planet formation.

In the afternoon, I went to the COSMOS session. I have a soft spot for the COSMOS project since it was my first real introduction to astronomy; the summer I spent at Caltech in 2004 was centered on playing with all of the HST COSMOS data that was available at the time (about half of it). It's a gorgeous data set. Apparently the S-COSMOS data set, the Cycle 2 Spitzer data of the COSMOS field, is now available. Many of the talks were about these infrared bright galaxies, though the talk I found most intriguing was the one on asteroids found in the COSMOS field with Spitzer: one person's trash is another's science.

After all of the talks, I went over to some nearby beach with a group of graduate students mostly from the University of Hawaii. Yesterday being Memorial Day, there was a Lantern Floating ceremony; people light little lanterns on little boats in remembrance of lost ones, and at sunset let them out into the sea. There was music and ceremony and many many people. I took lots of pictures, but none of them are very good. I didn't care much for the overly fancy rituals projected onto the big screen by the people running the shindig, but watching the people who had brought their own personal lantern boats walk to the ocean, I think I like this way of honoring and remembering the dead. As the sky grew darker, the water became more and more littered with bright lights.

Day 0 at the 210th AAS: Honolulu!!

I flew in yesterday afternoon via Chicago on American Airlines. It was a 9 hour flight, and yet they didn't have any food resembling a meal back in steerage class, just things like overpriced chips and overpriced cookies and sodas. I guess I've been spoiled by the only four hours longer trans-Pacific flights where they have two real meals, as well as snacks. So when I arrived at the hotel yesterday afternoon, I didn't know if I was more hungry or more tired.

I've never been to Hawaii. It's 7 a.m. here, six hours behind the east coast of the continental US. This kind of jet lag isn't so bad, as I can both sleep for a long time (still recovering from a cold) and feel like I'm getting ujp early. From my hotel room (which comes with a nice balcony!), I can see two moutains with either really thick fog or rain between them. From what I've seen so far (airport, mall, convention center), this is a really indoor-outdoor place; I like it. I like how I can not realize that I'm outside until the ceiling above me disappears.

Last night there was a small reception on the roof of the convention center. This is another way of saying, there was a small amount of food, but enough to make me not want to go foraging for a real meal. I only keep mentioning the food because I really haven't eaten since like Saturday, but I'm not a breakfast person, so I still don't feel like eating now. Anyhow, I met a group of people from the University of Texas, a girl who plans on conquering the infamous eigenvector 1. In the increasing darkness over dumplings and fresh fruit, we discussed said eigenvector and other AGNy things like the broad-line region, FeII, FeVII, and NeV, with Greg Shields and Richard Green. I sometimes wonder what's going through people's minds when they ask me the simple question of what I work on, and I stammer a little, explaining that I am presenting here on variable stars at the Galactic center,
but now I'm working on the Lyman-α forest. Do I seem well-rounded, or indecisive and noncommittal?

Today is the first day of talks and posters. The posters will be up in two batches; the first batch today and tomorrow, and the second batch Wednesday and Thursday. Mine is in the second batch. There are several simultaneous talks I know I will want to go to, and I haven't decided which I'll actually go to yet. One thing people always complain about with the AAS meetings is that they are so big; talks are limited to 5 minutes each (and, of course, people routinely go over, which mostly serves to annoy the audience and the moderators). The irony is that since the meetings are so big, no one comes. They say it's good for undergrads and graduate students (and, to an extent, postdocs) to go and meet people, but if no one who "matters" goes, then who is there to schmooze with?

A much more relevant question, though, is whether I give this post an EST or an HST timestamp.