Friday, December 28, 2007

What it's like to observe at a major telescope

A new Youtube video describes what it's like to do observing at Mauna Kea.

Wednesday, December 26, 2007

Galactic Evolution

Blogging on Peer-Reviewed ResearchWe all know how much of a fit creationists throw over biological evolution. We've also seen just how much of a fit they throw fits over stellar evolution. But there's change on even bigger scales as well.

From Brahe’s observation of a supernova in 1572, to Arp’s catalogue of odd an interacting galaxies, to Hubble’s observation of an expanding universe, it has become quite apparent in the history of astronomy that we live in a dynamic universe; it evolves. However, the evolution of some systems is easier to trace than that of others. With stars, we can observe clusters, in which only the mass of the various components differs significantly, in order to test our theories of stellar evolution. Unfortunately, for systems as large as galaxies there is no analogue.

One of the main reasons for this is a difference in the way stars evolve as compared to galaxies. Most stars are, for all intents and purposes, isolated systems, separated by vast interstellar distances. Even for the rare stellar systems that are close enough to undergo some sort of transfer, these amounts are typically only fractions of the mass of the objects. Thus, the evolution of stars is governed primarily by internal forces. While galaxies have gas and dust by which they can change their properties by making new stars and building heavier elements, galaxies are never observed in complete isolation. They are always members of some cluster in which interaction is inevitable.

As such, galaxies are not only subject to internal forces, but are also acted upon by external forces when they interact with other galaxies through glancing blows, mergers, or even cannibalization. This is true even in our own galaxy. While our nearest major neighbor may be quite a ways away, the Magellanic Clouds as well as several recently discovered dwarf galaxies swarm around us.

The current theory of galactic formation is that early in the universe, star formation began in smaller systems, which accreted into larger systems as the universe aged (Wiklind, 2007). As such, we would expect massive galaxies to be more prevalent at low redshifts. However, recent studies such as one by Wiklind et al (2007) looking at galaxies in the HDF, have shown that many massive galaxies with aged stellar populations exist at redshifts > 5, indicating that star formation occurred within a few hundred million years of the Big Bang.

For the first time, with larger and more advanced telescopes, are we able to peer back through true cosmological time scales to begin to see how galaxies have evolved as the universe has aged. Powerful new surveys, such as the Cosmological Evolution Survey (COSMOS), are new letting us place constraints on fundamental questions about how galaxies evolve. Questions of the evolution of the number density, when periods of star formation occurred, morphology, and chemical evolution can now be explored.

Mass Accumulation
Since, as previously mentioned, one of the driving forces of galactic evolution is that of accumulation of additional matter, it is of interest to study how this process occurs. This accumulation primarily occurs in two ways. The first is through the accretion of matter from the intergalactic medium (IGM). The second is through mergers with other galaxies that have already formed. The importance of each of these depends on the properties of the local universe at the time. If a great deal of raw matter is still available in the IGM as compared to the number density of galaxies, then the former process will dominate.

Fig 1. Fraction of bright galaxies in close pairs (5-20 kpc) vs (1 + z) for COSMOS field. Vertical error bars are 1σ. Star indicates local fraction. (Kartaltepe, et al., 2007).

One way this question has been approached, is to analyze the number of galaxies in close galaxy pairs at various redshifts. This method was undertaken by Kartaltepe et al (2007). By analyzing 1,749 galaxy pairs from the COSMOS field and comparing the number of paired galaxies to the overall number, they determined that the number of galaxies in close pairs increased significantly throughout the history of the universe (see Fig 1). Their study extended to z ~ 1.2, but they suggested that if the trend were extended to a distance of z = 2, it would indicate that nearly 50% of galaxies were in pairs during that time. However, little has been done in terms of high quality investigations for such limits.

Another interesting study indicating that mergers can strongly influence the properties of galaxies examined the density of galaxies (Trujillo et al, 2007). They found that, at redshifts of ~2, galaxies existed that had a density almost two orders of magnitude higher than any found in the present universe. Because of this, they suggest that such compact galaxies must have merged with others.

But mergers are not the only form of mass intake which galaxies can undergo. Accretion of matter from the IGM also plays an important role. Simulations by Semelin and Combes (2005) have indicated that mass gained via accretion exceeds that of mergers by a factor of 2 to 4. Before z ~ 2, the importance leaned more towards the factor of 4 while more material was still available. After that time, accretion should have become less important. This is somewhat supported by a study done by Netzer and Trakhtenbrot (2007), which looked at the growth time of AGN at z < 0.75 due to accretion and found that the amount of time they should have formed in is older than the observed age of the universe, thus agreeing with the conclusion that the rate of accretion is decreasing towards present time.

Star Formation & Luminosity
The process of adding more material almost certainly induces periods of star formation in galaxies. Accretion passively provides new raw resources; mergers and close encounters provide perturbations necessary to trigger collapses, and can have dramatic consequences, as demonstrated by the M81 group. Where new star formation occurs, so is there an excess of luminous stars, brightening the overall galaxy. Thus, if there is a correlation between the amount of mass and methods of gain through cosmological time, there must also be a relation to luminosity.

Fig 2. Star formation rate at 1,900 Angstroms as a function of resdhift (Bouwens & Illingworth, 2006).

To investigate this, many authors begin by examining what should be expected photometrically from a passively evolving galaxy in which no new star formation is taking place. Observations are then compared to this standard. In this area, studies have indicated that more massive galaxies (typically taken to be M > 1011 MSun) show less evidence for luminosity evolution than their lower mass counterparts (Bower, Lucey, & Ellis, 1992). This suggests that the most massive galaxies underwent a large burst of star formation early in the history of the universe, but have not done any significant star formation since that time.

In other cases, significant evolution is frequently noted. A study by Dahlen et al (2007) investigated the star formation and luminosity functions for lower mass galaxies. They concluded that star formation rates have been increasing towards present time and that specifically, in the spectral regimes they examined, this led to an increase of nearly 1 magnitude since z ~ 1.73. Their survey did not extend past this redshift, but other studies have indicated that there may well have been a peak in the star formation rate near z ~ 2. This was the conclusion reached by Bowens & Illingworth (2006) and is illustrated in Figure 2.


Fig 3. Size - redshift relation for disk galaxies selected by absolute magnitude. Blue dots show the median value in each redshift bin used. The solid line shows the best-fitting size evolution (1+z)1+m, where m = 1.1. Also shown are theoretical curves if sizes evolve as r is proportional to H(z)-1 (dashed line) and r proportional to H(z)-2/3 (dotted line). (Dahlen et al, 2007).

Another consequence of the evolution of galaxies is that morphologies will change as galaxies evolve. While morphologies can dramatically change due to interactions mangling structure, morphology can also be driven by more quiescent processes, such as the location of star formation. Such an investigation was also carried out by Dahlen et al (2007). They discovered that the number of galaxies with structure dominated by their bulges drops, approaching present time, from an average of ~10% of galaxies at z ~ 0.5 to ~30% at a redshift of 2.2. They also find that the overall size of galaxies has been increasing towards the present, as illustrated in Figure 3.

Meanwhile, in the arena of morphological evolution, there seems to be a more questionable relation to mass and limits of evolution. According to Conselice et al (2007), galaxies with masses of 1011 MSun are observed to have a consistent fraction of ellipticals (~70-90%). Other studies, such as that of Cresci et al (2006), have also indicated that massive galaxy morphology may be more stable over long periods. However, for galaxies above 1011.5 MSun they discovered that there has been a ~20% increase in frequency of such galaxies since z = 1.2. Additionally, there has also been an increase in the frequency of the 1010 MSun spiral galaxies since the same time, where peculiar galaxies of that sort have decreased in commonality. These findings are shown in Figure 4.

Fig 4. Frequencies of various types of galaxies vs. redshift for two binnings of mass. (Conselice et al, 2007).

It should also be noted that there is a strong correlation between galaxy morphology and the number of other galaxies in near proximity. Galaxies in clusters are significantly more likely to be of the “early type” (elliptical and lenticular) than a typical field galaxy (Smith et al, 2005). As with most other properties, we may ask whether this correlation also evolves. The findings of Smith et al (2005) suggested that for most clusters, the likelihood of a particular galaxy being early type is roughly constant over the past 7 Gyr. Only the densest clusters they studied showed strong evidence of any evolution of frequency.

Chemical Evolution
As stars are formed and die, they inherently enrich their host galaxies. From my review of the literature, it appears that most of the investigation into this topic has come in the form of modeling and very little has been applied in the way of constraints. One of the few studies that does make this attempt is that of Fritze, et al (2002). They applied observations of Damped Lyman α Absorber (DLA) galaxies to various models for the chemical evolution of spiral galaxies. They concluded that these early DLA galaxies followed the general trend set forth by models, suggesting that they may well be progenitors of spiral galaxies we see in the universe today.

In this post we have investigated four major galactic properties as a function of redshift in order to infer the manner by which galaxies evolve with the universe. It was shown that the number of galaxies in close pairs has been decreasing as the universe has aged. Star formation has also been decreasing in recent cosmological times, after apparently having a peak near a redshift of z ~ 2. The issue of morphology tends to be somewhat more difficult to untangle, as many factors seem to have an effect on this property. In general, galaxies around 1011 MSun seem to be somewhat resistant to morphological evolution, although more massive galaxies seem to be susceptible. While chemical evolution also undoubtedly occurs, little seems to be available in the literature as to how this has related to redshift for various types of systems.

In general, evolution is an important a force in the universe at large as it is for life on Earth. It sculpts galaxies and makes them shine.

-Bouwens, R. J., Illingworth, G. D., 2006, Nature, 443, 189.
-Bower, R. G., Lucey, J. R., Ellis, R. S., 1992, MNRAS, 254, 601.
-Conselice, C. J., 2007, MNRAS, 381, 962.
-Cresci, G., et al, 2006, preprint, arXiv:astro-ph/06072212v2.
-Dahlen, et al., 2007, ApJ, 654, 172.
-Fritze, U., Alvensleben, V., Linder, U., Fricke, K. J., 2002, Cosmic chemical evolution. Proceedings of the 187th Symposium of the International Astronomical Union, held at Kyoto, Japan, 26-30 August 1997, 147.
-Kartaltepe, J. S., et al. 2007, ApJ, 172, 320.
-Netzer, H., Trakhtenbrot, B., 2007, ApJ, 654, 754.
-Smith, G. P., et al, 2005, ApJ, 620, 78.
-Trujillo, I., et al, 2007, MNRAS, 382, 109.
-Wiklind, T., et al, 2007, preprint, arXiv:0710.0406v1

Only another year away

Apparently 2009 is now the official International Year of Astronomy as dubbed by the UN to celebrate the 400th anniversary of Galileo pointing a telescope up instead of through window of the neighbor girl. Sounds like it should be pretty fun. Not that astronomy's not fun without getting a bit of extra recognition, but this is a bit of welcome news given that the UK astronomy program has been hit with budget cuts and our administration isn't well known for its support of science. Hopefully, this will dredge up a bit of public support.

Tuesday, December 25, 2007

Happy Whateverday!

It's been a rather busy last few days. I just got home in time to do a bit of shopping before the holidays. As I was out and about, it continually struck me, just how imagined the "War on Christmas" really is.

When driving, I tend to listen to classical music. The St Louis station (99.1 FM) declared itself "The spirit of St Louis Christmas". At Borders, the cashier wished me a "Merry Christmas" and I didn't punch him in the face or sue him (like good atheists are supposed to I suppose). At Best Buy, a large sign hung from the ceiling wishing shoppers a "Merry Christmas." Most of the churches I drove past on the way home had out their nativity displays.

So merry and a happy New Year!

Tuesday, December 18, 2007

Good Idea/Bad Idea

I'm always a fan of taking superstitious nonsense and replacing it with rational options, so in a sense, I'm quite happy to see this presentation by the Morehead Planetarium in North Carolina, in which they address the mythical Star of Bethlehem. However, if they're going to try and do such a thing, they should at least make sure to get the science right.

The article says it explores possible "astronomical explanations for the Star. Viewers can decide for themselves whether a blazing comet, an exploding or shooting star, a major eclipse, or a conjunction of planets might explain the reported event."

Seriously. A shooting star? Why is this even being brought up as a potential option. Shooting stars are meteors that zip across the sky in often less than a second. I hardly see any magi being able to chase that down.

The rest of their options have a similarly pointless approach. If it's anything outside our own atmosphere, then it's going to move. Funny that whole rising in the east, setting in the west thing. The only way something like that could not move (and thus allow the wise men to be able to follow it) was if it were near the North Celestial Pole (i.e. Polaris, the North Star).

This would rule out anything in our own solar system since the NCP is pretty far away from the plane of the solar system. Thus, about the only viable astronomical events left are novae (including the super variety). This sounds pretty good to me. A supernova in our galaxy could well be near the NCP.

But there's still another glitch. It would always look like it was still further North. Matthew 2:2 says:
"Where is the one who has been born king of the Jews? We saw his star in the east and have come to worship him."
So it looks like that's not going to work either. Additionally, such an event would have been visible in many more places and there are no other historical records confirming what would undoubtedly have caused a stir.

"Star in the east" does have somewhat of a familiar ring to it though. Since things rise in the east, the east is the direction by which morning comes. The planet Venus has two other names: Lucifer and Noctifer. The former means the morning star, whilst the latter means the evening star. Could it be possible that Venus was the "star" they observed since when it appears in the east, it only rises a relatively short distance before the sun rises? Sure. But only if you want to believe that ancients were completely ignorant of Venus before hand. Other sources have pointed to Jupiter, another planet that often appears as a bright star like object in the skies. But I would dismiss this for the same reason. Both Venus and Jupiter (although not understood) were familiar astronomical sights and both would have been visible either before or after (depending on whether or not it was in retrograde motion) ruling out the notion that it could have been a novel event.

Thus, the Star of Bethlehem does not have a good astronomical explanation. But this doesn't mean there isn't a good rational one: It never existed. Like so much of religious history, this event is likely either an exaggeration or fabrication, much like Sampson killing 1,000 Philistines with the jawbone of an ass in Judges 15. But somehow, I doubt this is the track the planetarium show will be taking.

Instead, I suspect they will make the same conclusion I did in the first part (no credible astronomical explanation) but then given credence to the inane philosophy of "if we don't know, that means your nonsense is credible!"

Monday, December 10, 2007

Book Review - Myth of a Christian Nation

Not too long ago, CNN had a special entitled God's Warriors. During the segment on Christianity, one of the people they interviewed was a megachurch pastor named Gregory Boyd. Astonishingly, he was arguing against the notion that America is somehow an inherently religious nation and that pretending it is, is not only harmful to our country and constitution, but also harms faith.

So back in October I picked up a copy of his book The Myth of a Christian Nation (Subtitle: How the quest for political power is destroying the church). I've been slowly plodding through it over the course of the past month and a half and finally finished it a little over a week ago.

The main theme of the book is that trying to control people by legislating morality is antithetical to the entire premise of Christianity. He points out that Jesus, although living in a politically charged climate, did not weigh in on political issues or try to influence the government. Instead of exerting a "power over" mentality, he tried to change people by transforming hearts to influence actions in a "power under" mentality.

American Christianity, Boyd points out, does the exact opposite; They try to influence action to control hearts. As such, instead of getting Christians that actually follow the teachings of Christ and befriend the downtrodden, we get arrogant, self-righteous, pious pricks. No disagreement from me there!

He illustrates the proper behavior of a true Christian on pg 144 where he describes the plight of a pregnant, unwed teen mother who was afraid to tell her parents of her pregnancy for fear they'd kick her out. Instead, she confided in a close family friend that, instead of passing self-righteous judgment, offered to support her in any choice she made, shelter her if her parents did kick her out, and help pay for the child should she decide to keep it. As a result, the girl did end up keeping the child. Boyd describes this as being truly "pro-life".

Boyd makes several other good points to support his argument. Another one was on page 137 in which he argues that perhaps the reason that American Christianity is so obsessed with homosexuality, is that that is (typically) the one sin they don't have (although some people suspect that it's also flogged because so many are and they're trying desperately to deny it). As such, they focus on that one in an effort to ignore their own faults. Hypocrisy at it's finest!

Another example at the marriage of Christianity to American politics Boyd gives is that it has become popular to think of the enemies of America as enemies of Christianity. Freedom is assumed to be a "Christian value" (Boyd points out it's not), and thus, when terrorists are out to "destroy our freedom", it's not only a war on America, it's a war on Christian virtues and thus, Ameri-Christians become even more incensed. This obsessive, bloody devotion to the perceived virtues of religion is what perpetuates violence, Boyd argues. Although he didn't mention it, this isn't a new trend either. While fighting Communism, religion was again used as an excuse to further conflict. They were "godless Commies" and since we're the God minded people, we are more righteous, and thus, we need to slap God on our money and pledge! American values are Christian values. Don't believe me? Check the billboard. Instead, we allow these wars to be perpetuated in the name of our perceived religion. Boyd seems to want to think that for a "true" version of Christianity, this would somehow be a different case, but as Voltaire pointed out, "Those who can make you believe absurdities can make you commit atrocities." After all, how many wars have been perpetuated in the name of Atheism? As Boyd puts it, it's hard "to motivate one group to kill another and be willing to be killed by others without convincing them that there's a religious dimension to their tribal cause." (p 100)

While I was reading much of this book, I happened to be listening to the cast recording of Les Miserables, and much of what Boyd was saying made a great parallel to the plot. For those that aren't familiar with Les Mis, it's partially the story of a sinner, Val Jean, who is released on parole, and then steals silver to sell from a pastor that took him in when no one else would. He is caught and instead of piously condemning Val Jean, he tells the officers that he gave Val Jean the silver in order to start a new life, "buying his soul for God." It struck me that this is precisely the point Boyd is going for. Had the pastor turned Val Jean away as so often happens, he would not have been saved and thus, no further good could come. The tit for tat, eye for an eye system would be preserved.

So this was the main theme of the book: American Christianity isn't real Christianity because they go for the bloody "kingdom of the world" mentality rather than the "kingdom of God." Americans are no more Christian, more pious, more pure, than the rest of the world. We just like to think we are. Boyd even goes so far as to admit that most American Christians "lack even an elementary understanding of the faith they profess." This is clearly stated in the first chapter, but then repeated in slightly different ways for nearly 200 pages. I have to sometimes marvel at how amazingly dense the average Christian must be if a pastor feels that he has to repeat himself for 200 pages to get a single point across.

Regardless, the main premise of the book was one that I could agree with. I'd love to see some Christians that were more humble and not condescending asses. If they wanted to actually be nice and try to "transform my heart" or whatever nonsense they'd like to call it, they're more than welcome to try, although I doubt it will get them anywhere.

But although I agreed with the main premise, this doesn't mean that there weren't things that Boyd said that I found either disturbing or flat out wrong.

One of the things Boyd constantly calls for is more prayer. Not the government sponsored type that so many Ameri-Christians are clamoring for, but personal prayer. He points out Americans "place more confidence in our individual and corporate political activity than [we do] in prayer (p 119)." On pg 177, he suggests that one person praying does more than an entire army. Instead of participating in the Civil War to end slavery, he suggets, we should have prayed our way out of such a large conflict. This is nothing short of complete stupidity given that studies have shown that prayer does not work. As the adage goes, "One pair of hands at work does more than a thousand clasped in prayer."

Boyd also argues for blind faith and ignorance. If you trust "worldly effectiveness" over "kingdom faithfulness", then it is a sign that you are relying too much on "common sense." Get that? He explicitly says that if you follow what works there is something wrong with you! Instead you should blindly follow your faith.

This is just part of the Christian mindset that should seriously disturb any right-minded person. Another aspect Boyd argues for is that Christians should make sure they're persecuted because "as terrible as they often are, persecutions have usually had a positive kingdom effect (p 181)." I think I'll have to go with Charles Bradlaugh when he said, "I cannot follow you Christians; for you try to crawl through yourlife upon your knees, while I stride through mine on my feet."

Overall, the book made a point that I think should be taken to heart by Christians. If Christians actually practiced what Boyd preaches, I wouldn't have nearly as much of a problem with them. However, it's just replacing one form of nuttery with a less offensive, but no less crazy form. In fact, it seems to me that Boyd's form is more ludicrous when it advocates giving up rational thought for faith, but at the very least, it's certainly less dangerous to our Constitution and to the world in general.

Friday, December 07, 2007

Sleep is awesome

After having nearly a dozen assignments due this week, between term papers, lab reports, general homeworks, projects and presentations, I'm finally finished. Oh it feels nice.