Monday, September 15, 2008

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.

Monday, September 08, 2008

Book Review: Halima Bashir's Tears of the Desert

Over the weekend I read Tears of the Desert: A Memoir of Survival in Darfur by Halima Bashir.

Tears of the Desert details the life of Halima Bashir, a doctor who grew up in Darfur and now lives in the UK. Her story is told in a straightforward manner: how she grew up and how her family and village were important to her, how she went to school and enjoyed it and eventually went on the medical school, how war crept into her life until it became un-ignorable and eventually destroyed her life, her home, her family, and how she finally escaped from Sudan and managed to put together a new life in England. It most places—even the childhood stories—the story is riveting (which, unfortunately, also means that some of the explicit statements of foreboding come across and cheesy and unecessary). The storytelling is also often unexpectedly hilarious; I found myself laughing out loud quite a few times.

As a personal accounting of the history of the Darfur conflict, Tears of the Desert is a powerful story of how innocent lives are completely torn asunder. Bashir has lived through things that most of her readers cannot possibly imagine (yet, of course, as the book is written in the first person, we the readers know that, she at least, has survived). Her story thrusts raw emotion into the too easily glossed-over refugee and death statistics streaming out of the region. However, I found the book almost too insular at times; for example, the only year explicitly stated (aside from in the short epilogue), is the date of Bashir's birth: 1979. I was constantly adding and subtracting to determine approximate dates, and so as an actual history Tears of the Desert unfortunately falls a little short and does not serve well as an introduction to the Darfur crisis, and I fear that in ten to twenty years this fact will make it an even more difficult read. Likewise, no map is offered and only a brief description as to the underlying cause of the conflict and why the UN is doing little to stop it is given in the epilogue.

Regardless, a reader who first spends half an hour reading about the Darfur situation online should have plenty of context in which to set this book, and Tears of the Desert provides a far more personal and accessible accounting than anything the internet (or most anywhere else) has to provide.

Tears of the Desert will be on sale in the US on September 9, 2008.

Sunday, September 07, 2008

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.

Friday, September 05, 2008

Citations and Paper Length

Interesting paper on astro-ph this morning from Kris Stanek. As it turns out, in general, longer papers tend to get cited more. The exception is that, in astronomy, two of the major journals have a "Letters" section, which limits papers to 4 pages. These Letters do tend to be cited more than other short papers (presumably because they are Really just longer papers squeezed into a shorter format). Thus the graph of number of citations versus page length looks an awful lot like the state of Ohio:
The paper also includes some silliness-tinged career advice.