1 teacher + 1 astronomer = Project ASTRO

Until a couple of weeks ago, I hadn't heard about Project ASTRO. So what is Project ASTRO? Let me use the words of the Astronomical Society of the Pacific who founded the project in 1994: 

"Project ASTRO™ is a national program that improves the teaching of astronomy and physical science by linking professional and amateur astronomers with local educators. Each astronomer is matched with an educator in a one-on-one partnership and commits to visiting the educator’s students at least four times during the school year. [...] The main focus of Project ASTRO educator-astronomer partnerships is hands-on, inquiry-based activities that put students in the position of acting like scientists – as they come to understand more about the universe (and science in general)."

Since its foundation nearly 20 years ago in the San Francisco Bay Area, the project has spread it wings and local partner sites have popped up all over the United States. Currently, there are more than 500 astronomer-teacher pairs who advocate astronomy and scientific thinking to more than 20,000 students per year.

Project ASTRO workshop

One of the local partners is NOAO in Tucson, AZ. Each year several introductory workshops are held for the teachers and astronomers. About 2 weeks ago I attended such a 2-day-workshop for Project ASTRO at NOAO as an astronomer, to be paired up with a teacher. 

Demonstration of the power of the sun using a Fresnel lens to
melt metal. All images credit: Janine Pforr

After the initial introduction, the workshop was packed with a variety of presentations and hands-on activities to illustrate to both teachers and astronomers the diversity of provided materials and lessons plans which can be used in the classroom and even for field trips.

Demonstration of the power of the sun:
the metal is smoking after a few seconds!

The kick-off activity for the teachers at the workshop was to sort the lunar phases into the right order using little pictures of the moon. Later the concept of the moon phases and their cause was illustrated using a bright lamp (a.k.a the sun) in the center of the room and "moon balls" held up by each of the astronomers who orbited around their teacher partner. This was also a great way to visualize the concept of solar and lunar eclipses. Since it was a sunny day, we also had the chance to observe the sun and some sun spots with the help of "sun spotters" and special solar telescopes equipped with filters to protect man and instrument (NEVER look at the sun without protection!). Then we got a live demonstration of the power of the sun from 2 workshop helpers ala "frying ants with a magnifying glass" just without ants, we are animal-friendly. The picture shows you how they managed to melt metal using the sun's rays and a special lens, called a Fresnel-lens, but don't try this at home, you could seriously injure yourself or others!

Tucson's nightly glow as seen from Kitt Peak Observatory.
This is what's called light pollution.

Another activity on day one illustrated the importance of a dark sky for astronomers and how light pollution has become more and more of a problem over the last decades. Light pollution means that due to artificial light sources at night, such as street lamps, neon signs etc, one is less and less able to see the band of the Milky Way and stars in the night sky because they are a lot fainter than light sources on the ground. In the picture on the right you can see the glow of Tucson at night as seen from Kitt Peak Observatory located about 80 miles to the Southwest. Now, Tucson is already a lot darker at night than other cities due to the light pollution consciousness for the nearby Observatory, but you can still see a lot of it. If you want to participate in logging light pollution, check out the Globe at Night website!

Meteorites at the LPL meteorite collection

As I mentioned above, Kitt Peak Observatory is really close. In order to give the teachers an idea of the observational side of astronomy the afternoon and evening of the first workshop day featured a trip to OSIRIS REx and Kitt Peak.

4-m Mayall Telescope at Kitt Peak Observatory

First stop was a visit to the OSIRIS REx (of course an acronym; it stands for Origins Spectral Interpretation Resource Identification Security Regolith Explorer) mission building in Tucson which is part of the Lunar and Planetary Laboratory (LPL) of the University of Arizona. In brief words, the mission plans to send a spacecraft to a nearby asteroid, observe it for a while, then snatch some material off it and bring it back to Earth. The data collected during this mission will then be analysed to help understand our solar system, life in the Universe and our risk of being hit by one of these asteroids. One of the astronomers working on this project showed us more details about the mission and its planning as well as some real meteorites found on Earth and some of them really were quite big! Currently, there is a naming contest underway to provide the asteroid that will be visited by the spacecraft with a more memorable name than the usual numbers and letters that get assigned to such objects. If you're under 18 and want to give it a try, check out details and rules about this contest!

On Kitt Peak, we got a tour of the 4-m Mayall Telescope and attended a nightly observing program as organised by the Kitt Peak's visitor center. The nightly observing program was divided into 2 parts. On the one hand, each participant used a star finder and constellations to orientate themselves on the night sky in order to find objects such as double stars, star clusters, and the Andromeda galaxy with binoculars. In fact, if you find yourself in an extremely dark spot at night, you can even see Andromeda with the naked eye! On the other hand, we looked through the visitor telescope at objects such as the Ring nebula, a left-over from a dying star.

The finished play-doh planets, to scale!

Day 2 of the workshop was all about scales in the Universe, particularly the solar system. First, the teachers were presented with an idea of the distance between the planets and their respective size using peppercorns and football fields under the hot Arizona sun. Then back inside they were guided towards modeling our planets with Play-doh, piece by piece, as shown in the picture.

After visiting the neighbouring Flandrau planetarium for a demonstration on available planetarium shows for groups, we finished the activities by making comets using dry ice, water and dirt (again: don't try at home!). The sizzling "comets" are shown below.

Left: cooking up comets! Right: a finished comet.

Finally, teachers and astronomers had the chance to exchange expectations to the program and their Project ASTRO partner and started planning some of their activities and visits. The stone for a lot of activities, like star parties, is rolling and we will report back to you from some of these. For now, I am looking forward to working with my teacher and seeing the excitedly-glowing eyes of the school children when I tell them about our solar system, galaxies and the Universe! 

When Theory Meets Observations

This summer around 30 astronomers met for the CANDELS Theory Workshop, held from August 8-10 at the University of California, Santa Cruz. This was a smaller event than the recent CANDELS team meeting, with most researchers working in one or two subfields in extragalactic astronomy. The meeting wasn’t limited to just theorists however; in fact much of the discussion centered around how we could use CANDELS observations to better constrain theoretical models of galaxy formation.

Most of the presentations centered around two theoretical tools: semi-analytic models and hydrodynamical simulations. While both of these are computerized models that predict the properties of galaxies, they have vastly different approaches.

Hydrodynamical simulations 

Hydrodynamical (‘hydro’) simulations are high-resolution, detailed simulations of the formation of galaxies. While stars and dark matter are simulated with particles, we use a technique known as Adaptive Mesh Refinement to trace the movement of gas, dust, and metals throughout a galaxy. Areas of greater density – those that are more likely to have interesting physics going on – are simulated in greater detail while regions with little gas or stars are treated with less refinement.

One of the major discoveries from these hydro simulations has been the formation of stellar clumps in high redshift galaxies. Most of the ‘classical’ images we have of disk galaxies such as our Milky Way or the nearby Andromeda Galaxy show regular spiral structures. At higher redshifts however, the picture is murkier. Galaxies seem to have large clumpy regions embedded within their disks.

Galaxies at high redshifts tend to have clumpy structures. Since these galaxies are far away, individual features of the galaxy are harder to resolve. Shown here are images of 6 galaxies taken with two CANDELS filters. Image credit: CANDELS collaboration, http://candels.ucolick.org. 

Naturally, both theorists and observers would like to understand how these clumps form. Are they remnants of small galaxies swallowed up in mergers, were they accreted from the cosmic web, or do they form within the disks themselves?

An advantage of hydro simulations is that we can study these processes directly and watch them evolve over time. A team of theorists, led by Professor Avishai Dekel has been doing just that. Dekel’s team has found that about 2/3 these clumps formed in-situ, while the rest joined the galaxy through a merger. Furthermore, clumps that formed in-situ tend to be less massive and contain younger stars – all tantalizing predictions that may be confirmed with CANDELS data.

A high-redshift galaxy from a hydrodynamical simulation. Regions with
redder colors have greater densities, and clumps have been outlined in
circles. The labels on the clumps indicate whether the clump formed
in-situ (is) or ex-situ (es). 
Image credit: Dylan Tweed, Hebrew University of Jerusalem

While hydrodynamical simulations can produce detailed images of galaxies, in some instances the simulations are actually too detailed. Real high-redshift galaxies are billions of light-years away from Earth and appear only as specks of light on even the largest telescopes. Furthermore, these galaxies tend to have a large amount of dust that scatters and absorbs their light, much like a car’s headlights are diffused by fog at night.

To compare theory and observations directly, we must mimic the effects of dust and simulate the blurriness and uncertainties introduced by a real telescope. To do this we use a tool called SUNRISE, which takes the raw data from hydro simulations and reprocesses it, projecting the information from three dimensions down to two and allowing for dust emission and absorption. We then create mock ‘observations,’ using simulated filters that match the real ones on Hubble.

This process, which we’re terming ‘Candelization’, is still a work in progress. The images we have so far however are strikingly realistic. In many cases, it’s hard to tell the difference between simulated galaxies and the real thing! Even though the hydro models only simulate dozens of galaxies, between the hundreds of possible camera angles and dozens of simulated filters, we can create a suite of thousands of images that can be directly compared to CANDELS observations.

A 'Candelized' simulated galaxy in three projections at redshift z = 1.70.  Note the clumpy substructure, and the red dusty region in the center of the galaxy.  Image credit: Christopher Moody, University of California, Santa Cruz).

Semi-analytic modeling

Instead of making a handful of galaxies in great detail, semi-analytic models (SAMs) focus on simulating thousands or millions of galaxies with very little detail. These two methods are often complimentary, and indeed many of the physical properties included in SAMs were first studied in hydro simulations.

Semi-analytic modeling uses simple physical approximations to predict the statistical properties of hundreds of thousands of galaxies. The first step is to construct a high-resolution simulation of the way dark matter forms structure. Since most of the matter in the Universe is actually dark matter, the galaxies we see are all embedded in large dark matter halos. These halos grow and merge over time, condensing along filaments and leaving voids where there is not enough dark matter to gravitationally collapse.

 

Visualization of dark matter structure formation from the Bolshoi Simulation.  The brighter regions have more dark matter, and are the regions where galaxies will eventually form.  Image credit: Chris Henze, NASA Ames Research Center.

Even though dark matter is only subject to the force of gravity, the sheer size of the simulation requires billions of particles each representing millions of solar masses. The CANDELS SAMs all are based off the results of the Bolshoi Simulation, which took over 6 million processor hours to run on a NASA supercomputer. 

The next step is taking all of the information from the Bolshoi Simulation and condensing it into a simple form for the SAMs to use. To do this, we construct ‘merger trees’ that record the masses, sizes, and positions of dark matter halos when they merge together. This retains much of the statistical information about dark matter structure – for example, how it clusters in space, how larger halos form from smaller ones – without having to keep information about every particle of dark matter.

Once we have a merger tree we take all of the dark matter halos at high redshift and ‘seed’ them with a galaxy. We then follow the merger tree over time. Whenever two dark matter halos merge we allow their host galaxies to merge as well, until the simulation reaches redshift zero. We then compare to well-known observational relations such as the galactic stellar luminosity function, which describes how many galaxies there are of a given luminosity within a chosen volume of the Universe.

As with most things, the devil is in the details. SAMs include prescriptions for most of the physical interactions galaxies are thought to undergo, such as the growth of black holes, reionization, the blowout of gas due to supernovae, and the formation of galactic disks and bulges. Since all of these areas are still the subjects of active research, many of the formulas SAMs use are educated guesses at best. 

Furthermore, to use a quote from Einstein, SAMs try to “Make things as simple as possible, but not simpler.” In contrast to the Bolshoi Simulation, which generated terabytes of data and took months to run, SAMs can simulate the evolution of hundreds of thousands of galaxies over all 13.7 billion years of the Universe overnight on a consumer-grade laptop! 

The advantage of being able to run so quickly is that SAMs can try out many different physical models in a relatively short period of time. We can pose simple questions – what if the star formation rate is dependent on the amount of metals in a galaxy? How does removing supernovae affect the stellar masses of galaxies? – modify the SAMs accordingly, and see what the results are.

The relationship between hydro simulations and SAMs. Plotted
is the correlation between galaxy mass ratio and the amount of star
formation in a merger.  Each point represents a measurement from a
different simulation of two galaxies merging, while the black solid and
dotted lines represent approximations used by many modern SAMs.
Image credit: Cox et al. (2008), MNRAS 384, 386

There is a tradeoff, however – you won’t see pretty pictures of galaxies generated from SAMs. Every ‘galaxy’ exists as a single line in a spreadsheet, detailing the general properties such as its size and its mass. But for questions where you need to simulate large numbers of galaxies to get an answer, SAMs are the way to go.

While these two approaches – hydrodynamical and semi-analytical – may seem to have nothing in common, many of the equations used in SAMs were derived from approximations to hydro simulations.  The physical processes that we can study in great detail in the hydro simulations should apply to galaxies in SAMs as well.

One of the major themes of the Theory Workshop was how to continue this interplay between hydro simulations and SAMs, and between theory and observations.  After all, at the end of the day we're all looking at the same fundamental questions: How do galaxies form, and how do they evolve over time?  We don't have all the answers, but with CANDELS the picture is becoming a little bit clearer.

The REU Experience and Working with CANDELS

My name is Erin O’Leary and I am an undergraduate student pursuing my bachelors in physics and astronomy. This summer I had the opportunity to join the CANDELS team working with Jeyhan Kartaltepe as part of the National Optical AstronomyObservatory’s (NOAO) Research Experience for Undergraduates (REU) program at Kitt Peak National Observatory. I thought I would take the opportunity to share with everyone the story of my summer and the experience I had working with CANDELS.

I am an undergraduate in my senior year finishing my astronomy degree at Macalester College, a small liberal arts school in Saint Paul, MN. Astronomy has been an interest of mine since I could check out stacks of space books at the public library. In high school when I realized I could make a career out of my interest in astronomy, my path was pretty much set.

I spent my previous summer conducting astronomy research at Macalester with Professor John Cannon. I analyzed the stellar populations within a nearby low mass galaxy. This was my first real taste of the research world, and I loved it! I thrived on the independence and the sense of depth that so is different from coursework. I decided I wanted to spend my next summer carrying out astronomy research at a larger science institution. Galaxies in particular piqued my interest and I sought a research experience where I could explore the topic further. I applied to many NSF funded REU programs across the country, and to my excitement, I was offered my top choice position at the KPNO REU!

2012 KPNO and NSO REU students at Kitt Peak

For twelve weeks I lived in Tucson, AZ (quite different than Minnesota!). I spent my time engaging in the undergraduate research experience, which included - yes - lots of research hours spent in front of a computer writing and debugging programs. But what is so great about REU programs like the one I experienced are the vast opportunities to gain exposure to other areas of astronomy and meet cool people. Tucson is a huge hub for astronomy, making it a great place to see all the areas of astronomy in action. Weekly we heard from NOAO or visiting scientists about their area of research. My fellow students and I had tours of the University of AZ mirror lab, NOAO’s optics lab, the McMath-Pierce, 2.1-meter, and the Mayall 4-meter telescopes on Kitt Peak, as well as a week of travel to New Mexico to visit the Very Large Array, the Sloan Digital Sky Survey, and the National Solar Observatory Sacramento Peak facilities. I also spent four nights observing on the 2.1-meter on Kitt Peak. Being able to see (and use) these instruments and then hear about the science resulting from these observations was truly inspiring! I gained so much insight into where my astronomy career can take me. 

Sunset over Kit Peak National Observatory this summer. 

Now onto my work with CANDELS! Before this summer, I had not heard of CANDELS. I was quickly amazed by the quantity of data and science coming out of this project, which made me even more excited to be part of it! 

As I mentioned above, my summer research focused on understanding the role that galaxy mergers and interactions played in galaxy evolution. A few related posts are here and here. Galaxy mergers are beautiful and dynamic phenomena and seen as important drivers of galaxy evolution. Merging galaxies are rare now, but are believed to have played a larger role earlier in the universe. My work involved identifying these galaxy mergers.

CANDELS data are unique and exciting in that they probe higher redshift objects allowing us to view light whose wavelength has been stretched in the expanding universe. What was once visible as optical light is now observable in the infrared. This is essential for accurate galaxy morphology classification. My project was a first look at galaxy mergers at higher redshift (greater than z ~ 1). This can also raise some difficulties in merger identification. As we look at higher redshift galaxies, signature merger features can become faint and more difficult to detect.

I began my work familiarizing myself with the mechanisms of galaxy evolution, galaxy morphology classification, and the scheme that CANDELS has adapted in classifying morphologies. It was a flood of new concepts to me. I spent a fair amount of time classifying these galaxies and debating with myself whether something constituted a merging system. Simply the number of galaxies we were dealing with and the uniqueness of each galaxy blew me away. 

CANDELS images showing a sample of visually identified galaxy mergers.

I then set to work on analyzing the results of the visual morphology classifications of the CANDELS data covering the GOODS-South field. This is a catalog of 7,628 galaxies, each classified visually by about 3-6 people, which means a lot of things to keep track of! Sorting through the data, it was fascinating yet frustrating to compare the classifications that each person had assigned to a given galaxy. 

From this data set, I created selection criteria to choose systems that were merging. Visually, mergers appear to have undergone an interaction evident by an irregular structure, tidal features, double nuclei, or asymmetries. We selected a conservative catalog of galaxies we were pretty certain were mergers. For each identified galaxy merger we collected additional information by matching them to their redshift and mass. We looked for trends in the mass, mass ratio (for interacting pairs), and redshift to tell us about our merger sample.

It is satisfying to look back and see how much I learned this past summer. I felt that my work was just a tip of the iceberg. It was difficult to part ways with my project after those 12 weeks when I knew there exists so much more data and discovery on the horizon. With four more CANDELS fields, it will be very exciting to hear about future outcomes!

So what’s next for me? I am spending my current semester studying abroad at the University of Oslo in Norway and using the opportunity to squeeze extra astrophysics courses into my undergraduate years. When I return in January, I will present my summer research at the AAS meeting in Long Beach, CA. This will be followed by graduation in the spring of 2013. My future plans certainly involve attending graduate school for astronomy.