The Bright Galaxies that HST Can Barely See

The large number of galaxies that are clearly detected in the deep HST/CANDELS images enable us to carry out very exciting studies that we regularly report in this blog. Today, instead we will focus on a special type of galaxies that are very faint in all the CANDELS images, but at least 40 times brighter at longer wavelengths, in the so-called mid-infrared regime. Until very recently, only a few isolated cases of these galaxies were known, but thanks to the depth of the CANDELS data, and making use of mid-infrared Spitzer Space Telescope images, we have discovered 25 such galaxies within a single CANDELS field.

Since its launch in 2003, the Spitzer Space Telescope has allowed us to study, in a systematic way, the infrared emission of galaxies at different cosmic times. With respect to previous infrared observatories, Spitzer represented a major step in infrared astronomy, which was possible thanks to the fast progress of infrared detector technology over the last three decades.

Four examples of sources that are bright in the Spitzer Space Telescope mid-infrared
images, but very faint in the HST/CANDELS images. The multi-wavelength analysis of these
sources indicates that they are very likely massive galaxies formed in the first two billion years
of cosmic time. Image credit: Caputi et al. (2012), ApJ, 750, L20.

At low redshifts, the Spitzer mid-infrared images trace the dust emission of star forming galaxies, which occurs after the dust is heated by the UV photons produced by the new stars. The UV photons that are the consequence of accretion of matter onto a galaxy's central black hole can have a similar effect, namely heating any surrounding dust and making it emit at mid-infrared wavelengths. But for high redshift galaxies, the mid-infrared emission seen in the Spitzer maps has a rather different origin: it directly traces the redshifted light of the galaxy oldest stars. The CANDELS images, in turn, show the redshifted light of a (high-redshift) galaxy's young stars.

By comparing the multi-wavelength emission of our 25 Spitzer-bright galaxies with theoretical galaxy spectral models, we determined that the vast majority of these sources are very likely at high redshifts (z>3), which means that we are observing the light that was emitted by these galaxies when the Universe was less than two billion years old. Actually, nowadays we know many z>3 galaxies, but the properties of our newly discovered 25 galaxies are very special: the fact that they are bright in the Spitzer images, but much fainter in the CANDELS maps, indicates that these objects should be among the oldest and most massive galaxies to be found at such early cosmic times.

Finding massive galaxies in the early Universe has important implications for galaxy formation theories, which need to explain how such objects could have formed so quickly and efficiently only a few billion years after the Big Bang. According to our most-accepted cosmological model, the Cold Dark Matter model, galaxies are embedded in dark matter halos, and grow with them hierarchically, through mergers, from small to larger units, through mergers. In such a scenario, one would expect that massive galaxies are the last to form. But different astronomical observations  conducted over the last decade indicate that the most massive galaxies that we see in the Universe today basically finished their growth when the Universe was less than a half of its present age (this is 8 billion years ago), while less massive galaxies continued forming a significant amount of stars later. This phenomenon is what extragalactic astronomers call 'galaxy downsizing.' So, searching for massive galaxies further back in time is very important for understanding when galaxies could assemble a large mass for the first time in the history of the Universe, and thus constraining galaxy formation models.

Another exciting aspect of our new, massive galaxy candidates at high redshifts is that they potentially constitute the 'tip of the iceberg' of a  larger galaxy population that still remains to be discovered. To fully understand the importance of such a galaxy population we will have to wait for the advent of the HST successor, the James Webb Space Telescope (JWST), which is due for launch in 2018.  The JWST will provide us with much deeper images than current telescopes, thanks to its large collecting area  -- seven times larger than the HST, and almost 60 times larger than Spitzer. With these deeper images,  we will be able to search for fainter analogues of our galaxies at higher redshifts. In the meanwhile, we are trying to follow up our galaxies at far infrared wavelengths with the Atacama Large Millimetre Array (ALMA), which is the only instrument that, currently, can independently confirm the nature of our sources.

Ultraviolet Observations in CANDELS

The CANDELS project is primarily focused on observations at optical and near-infrared wavelengths, that is light that is received at the wavelengths that the human eye can see and a little bit longer. However, a fortunate trick of the Hubble Space Telescope (HST) orbit also allows us to observe one of the five CANDELS fields at ultraviolet (UV) wavelengths, that is slightly shorter wavelengths than the blue end of the rainbow. UV observations are especially interesting, because very massive, very hot stars emit light strongly at those wavelengths.

How We Get UV Observations

Optical HST image of the Hubble Deep Field (in gray scale) with
Far-ultraviolet observations over layed (in purple). The Far-ultraviolet
are wavelengths even further in the blue direction than the UV
observations planned for CANDELS. Most galaxies are not detected
in the far-UV, despite the image being very deep, because their light is
shifted redward by the Doppler shift ("redshift"). Image Credit: Harry Teplitz

HST orbits the Earth, which means that most of the time when it wants to point at an interesting position on the sky, it can only do so during a fraction of the orbit during which the Earth isn't in the way. There are a few places on the sky, though, for which HST can point continuously during the entire orbit. The GOODS-North field in CANDELS is one of these special places. This means that we have about twice as much time available to observe that field than usual. CANDELS uses some of the extra time to observe GOODS-North in the UV.

As with all CANDELS fields, GOODS-North is observed many times, building up the signal through repeated observations. The schedule of the repetitions is designed for the supernova search. In practice, this means that even though we got the first UV observations in the spring of 2012, it will be spring of 2013 before we have enough data to see most of the UV objects in the images.

Major Science Goals

The most massive, young, and hot stars emit light strongly in the UV. This makes UV observations particularly effective for studying galaxies that are forming many stars.  These data allow us to find these galaxies and to study how they formed.  

In a little more detail, we have three major goals for the UV observations:

1.  Finding and studying strongly star-forming galaxies:  

The most popular way to find distant star-forming galaxies is to look for a strong feature in the distribution of their light across the spectrum.  This technique, referred to as looking for the "Lyman break" or "dropouts", will be familiar to people who have read about the rest of the goals for CANDELS, because it is also used to find galaxies in the very distant Universe. The advantage of adding UV data to CANDELS is that it allows us to use the same method to find galaxies when the Universe was about 25% of its current age. And, by using the same technique to find them, we can compare those galaxies directly to the much more distant ones.
 

In practice, the "dropout" technique means that we look for galaxies that are bright in most of the CANDELS bands, but are much fainter in the UV.  That is, they "drop out" of the UV. This is an indication that the UV light that they emit has been absorbed by neutral hydrogen before it reaches HST.

Once we find these galaxies, we can ask many intersting questions about them: Do they tend to be big or small? Do they tend to have a lot of dust? Do they tend to be in groups together or are they isolated?  

2.  The build up of galaxy structure from sub-galactic clumps

Galaxies grow and develop structure over time. Through gravitational effects, possibly including merging with other galaxies, they become like the galaxies we see today. We know that they undergo periods of intense star formation, but we are still learning about how they form their distinctive structures like spiral arms.  

There is evidence that as many galaxies grow, they form small clusters of hot stars, which are often called "clumps", which then migrate together into larger structures. Measuring the number, size, and brightness of these clumps can help us understand how galaxies form their structure. It can also help us distinguish which kinds of galaxies form through the mergers of smaller galaxies, and which kinds form primarily by themselves.  

Clumps have been studied extensively in galaxies when the Universe was about 25% of its current age. UV observations, which will see the hot stars that make up the clumps, will allow us to study them in galaxies later in the histroy of the Universe, when it was around 50% of its current age.

3.  How does ionizing radiation escape from galaxies?

There was a period of time in the relatively early Universe, known as the "dark ages", when most of the electrons and protons in the Universe were together in Hydrogen atoms. When galaxies began to form, they emitted a lot of energetic photons (referred to as "ionizing radiation") which broke apart the Hydrogen atoms, an event called "Reionization." Exactly how this happened is one of the great mysteries of cosmology. In particular, we don't know how the photons got out of the galaxies that contained the hot stars that emitted them.

 
In order to figure out how this ionization radiation escapes, we need to be able to observe it. The best way to do this is to look at galaxies that are similar to those which caused Reionization, but are a little closer so that we can study them. 

The CANDELS UV observations will allow us to make some of the best measurements ever taken of ionizing radiation escaping from galaxies.

The Next Steps

CANDELS is currently taking UV images, with a single pass of the GOODS-North field once every couple of months. It will take about a year to build up enough of these images to reach the sensitivity needed for the science goals described above.  We are eagerly waiting for next year, when we can begin to look at these exciting data and see what we can learn about strongly star-forming galaxies, the build up of galaxy structure, and how ionizing radiation escapes from galaxies. Stay tuned!

How Old Are Galaxies?

"How old are you?" A simple question, frequently asked of children, but rarely asked of an adult in polite company. When we ask the question, we are asking for the number of years that have elapsed since you were born. But how old are you, really? There were nine months of cellular development before birth, so for some purposes, maybe we should include that. Also, the average age of cells in your skin is less than two weeks, your stomach cells are typically less than 5 days old, and your blood cells are less than 4 months old. The average age of all the cells in your body is less than 10 years. So how old are you, really?

Okay, so for humans, if you want to get persnickety, maybe age isn't such a well-defined concept, but still, time since birth is generally a pretty useful definition.

When did galaxies form?

Two nearby galaxies. At the center is an elliptical galaxy,
which is basically a ball of old stars. A spiral galaxy, similar to
Milky Way,  appears in the upper right. Spiral galaxies are
still forming stars today. Do these galaxies have the same age?
This turns out to be a tricky question to answer.
Image from the Hubble Space Telescope.

When does the clock start for galaxies? When I was in graduate school, there was a concept of the epoch of galaxy formation, when big galaxies started forming. This idea was largely driven by the observation that nearby elliptical galaxies - and the central bulges of spiral galaxies - are filled with old stars that are not organized into thin, rotating disks.  It seemed likely that this was because galaxies formed their stars before the gas had a chance to settle into a thin disk.

If galaxies formed fast, then they should have been very bright when they were forming all those stars. So bright that once telescopes were equipped with modern CCD detectors in the late 1970's, it should have been possible to see them at large distances. No one could find them. Astronomers found lots of little faint blue galaxies, but these were smaller galaxies, that were much closer to us than expected.

At about the same time that observers weren't finding the epoch of galaxy formation, theorists were developing the idea that galaxies formed hierarchically, centered on the densest patches of dark matter in the early universe.  These early galaxies started forming their first stars when they had acquired only a tiny fraction of their present day material. They subsequently grew larger as more gas fell in at later times, and when they merged with other galaxies. This hierarchical theory simultaneously explains why we couldn't find the epoch of galaxy formation and why galaxies cluster together on large scales.

The implication is that galaxies started out with very few stars, and may have taken a long time to reach their peak star-formation rate. That's indeed what we infer today when we estimate the average number of stars formed per unit volume in the universe. This cosmic star-formation rate peaked when the universe was about 3.5 billion years old, even though we have now found galaxies that existed when the universe was less than a billion years old.

Inferring galaxy ages from colors

Even though the hierarchical models have been several decades and we have known for more than a decade that the globally-averaged cosmic star-formation rate started out much lower than the peak rate, it has taken a while for astronomers to realize that when they try to infer the age of an individual galaxy from its colors, the traditional assumptions are probabably incorrect. The traditional assumption has been that the star-formation starts off high and drops off exponentially. This was motivated by the idea that a galaxy starts with a fixed reservoir of gas and its star formation must keep dropping as that gas is used up. These are known as "tau models" in the jargon (not this kind of tau model!), because the Greek letter tau is usually used to designate the timescale for star-formation to reach roughly half of its initial peak.  Recent studies have shown that analyzing galaxy colors using tau models can give very misleading estimates of star-formation rates and ages, and that adopting different models can improve the estimates. See, for example, papers by my fellow bloggers Janine Pforr, Stijn Wuyts and my former student Joshua Lee.

Star-formation histories of galaxies from a hierarchical model (blue), compared to the best-fit tau models that were inferred from the galaxies' colors. You can see that the tau models are not at all representative of the true star-formation histories. But the problem is that the blue curves are models too. For real galaxies, we don't know what the true answer is. What we need is simple models that work well for a wider variety of possible star-forming histories than the tau models. From Lee et al. 2009.

 

A new definition of age?

 

Back when it seemed reasonable to use tau models, it seemed reasonable to designate the galaxy age as the elapsed time since it formed its first stars. This would be equivalent to galaxy birth. But now that we know that galaxies formed slowly, it's much less obvious what we should use as an age. On the one hand, the "chemical evolution" of a galaxy - the build-up of the heavy elements created in stars - is highly influenced by the first few stars. Once the gas in a galaxy contains heavy elements, it's ability to cool to form stars is dramatically altered. So we are interested in when galaxies formed their first stars. But on the other hand, most of the stars in a typical galaxy didn't form until billions of years later.

When using galaxy colors to estimate ages, the simplest approach is to estimate when the galaxy had formed half of its present stellar mass. This is probably the most reliable estimate of age that we can make if we have nothing but the galaxies' colors to work with, and no particular preconceptions about their star-formation histories.  But this is like starting the clock when the galaxy was a teenager. It's also a peculiar definition in the sense that a galaxy's age will not increase linearly with time. In fact, under this definition, if a galaxy doubles its stellar mass every 100 million years, then it will always be 100 million years old. If it then suddenly doubles its mass in only 10 million years, it will become only 10 million years old. This can be a bit confusing.

Another possibility is to adopt a different set of models that might be more representative of the true star-formation histories of galaxies than than the tau models. We can then define age as the time since t=0 in those models, as was done for the tau models. Unfortunately, there is currently no consensus on what to use as an alternative model. This is a topic of debate and discussion at galaxy evolution conferences. Maybe this will settle out and we will all agree on how to set our clocks. Or maybe the consensus will end up being that age is not a useful concept for galaxies. It's too soon to tell.

So the question "how old is this galaxy?" turns out to be more subtle than we might have thought. Scientific progress is a continual process of unveiling our ignorance. Each advance in our understanding leaves us still ignorant, but ignorant at a much deeper level.

Meet Steve Rodney

From time to time we'll bring you a biographical post introducing one of the astronomers writing for the CANDELS blog.  This week, we introduce Steve Rodney.  You can find his earlier posts here.

View of Hanauma Bay on Oahu.

Currently I'm a postdoctoral researcher and a Hubble fellow at the Johns Hopkins University (JHU) in Baltimore, Maryland. Before landing here on the shores of the Chesapeake, I was a graduate student at the University of Hawaii Institute for Astronomy. Several of my classmates from Hawaii are also part of the CANDELS team: Dale Kocevski, Liz McGrath, and Jeyhan Kartaltepe were all Hawaii grad students while I was there. We're now scattered across the country, but team meetings give us the occasional opportunity to reminisce about shave ice, moonlight surfing, and Andy's sandwich shop. 

Me and the kids in Baltimore.

JHU is a great place to be, and I am very lucky to be working here with some fantastic people… but unfortunately living in Baltimore is a source of some significant environmental stress for me. Not because of the drugs and crime of Baltimore (excellent dramatizations notwithstanding, Baltimore is actually a great city to live in). No, I'm referring to the deep emotional trauma that comes from growing up a fan of the hapless Cleveland Browns, and now watching my 4-year old daughter wearing her Ravens jersey to pre-school. (If you're not an NFL fan, then think of the Ravens vs Browns as Manchester United vs Liverpool, but imagine Liverpool is hopelessly inept over many decades. If you're not a soccer fan either, then... well, nevermind). I can only hope that my daughter will eventually outgrow this phase of moral depravity.

One of the conversations that will come up for most any astronomer from time to time is the discussion of "Why astronomy?" Sometimes this is about personal choices: "Why did you choose to become an astronomer instead of a chemist or a doctor?" For myself, astronomy has always been a study that I was drawn to because of the stories. As a kid, I read the legends of Greek mythology, and was fascinated to find them echoed on the sky in the constellations. I loved to trace the stories of ancient heroes, gods and monsters that were painted across the heavens. Later, the study of physics opened up for me the fascinating stories within the stars, from the birth of a star incubated in a dusty envelope of gas, to the fragile beauty of stellar death throes. Studying astronomy takes these wonderful images and unfolds them to reveal the complex puzzles and deep mysteries of the universe. For me personally, this was the hook that drew me in. 

Cherry blossoms and the Jefferson
Memorial in Washington, D.C.

Sometimes the "why astronomy" question is framed more broadly: "OK, maybe astronomy is great for you, but what practical use does it serve in our society?" A glance at recent Nobel Prizes can illustrate this very legitimate question. Astronomers won a Nobel prize in 2011 for discovering Dark Energy. Exotic and fascinating, but also intangible and wholly disconnected from everyday human lives. In contrast, the recently announced 2012 Nobel prize in chemistry recognizes advances in the understanding of G-protein-coupled receptors (GCPRs). This work is fundamentally connected to drugs used in the treatment of a wide range of ailments, from common allergies and high blood pressure to breast cancer and schizophrenia. One might look at these two fields and legitimately question whether we as a society should be investing so much (both in dollars and in human capital) in the study of distant stars, when there are real problems with real people that can be addressed with other avenues of scientific exploration. 

I think this is an important question, and a conversation that we astronomers and fans of astronomy should have more often and more publicly. Especially in a time of tight budgets for research funding and significant skepticism about the value of science in general, we all should have a coherent argument for why basic research is important. For me, the answer is that the pursuit of understanding is a fundamental quality of humanity. What separates us from other species on this planet is our ability to consider the universe, to seek a deeper understanding of how it works and what is our place within the grand cosmos. In a way, astronomy is a bit like poetry, art and music. It is a discipline that provides its own reward by enriching our lives. We astronomers should never forget that it is a special privilege to be able to devote ourselves to this task, and that we have a responsibility to share what we learn with the world around us. 

Sunrise over Maui, viewed from Makapu'u point on Oahu.

How to Measure the Star Formation Rates of Galaxies

One important question that astronomers try to understand is when in the history of the Universe were the stars in galaxies formed. In order to address this question one can either measure the amount of mass in stars in each galaxy and analyze this as a function of time or age of the Universe. Or one can measure the on-going rate of star formation as a function of the age of the Universe. In this post I would like to focus on star formation rates and how astronomers can measure them. 

The current rate at which a galaxy is forming stars describes just how many new stars there have been born in a limited time period. When stars (or a stellar population) form from a molecular cloud one can (theoretically) count the number of stars with a particular mass and do this for a range of masses, meaning one (theoretically) knows the distribution of stars as a function of stellar mass. This is called the stellar initial mass function. Within this newly formed population of stars the most massive stars are the hottest and burn through their fuel the quickest which means they will live the shortest lives. The hottest stars are also the brightest. So if we can measure how many of the brightest stars there are we can determine the total number of stars that formed using the initial mass function.

Astronomers measure star formation rates with the help of a variety of wavelength ranges from the X-ray to the radio. All of these so-called star formation indicators probe the most massive stars. 

Pillars of creation, a site of star formation in the Milky Way,
credit: NASA, ESA, STScI, J. Hester and P. Scowen (Arizona State University)

Young, massive stars shine particularly bright in the ultra-violet wavelength range of the electro-magnetic spectrum. Naturally, this is the first wavelength range to consider for a measurement on the number of massive stars. Unfortunately, because stars form within and from clouds of gas and dust, the light that they emit is at least partially absorbed by the gas and dust around them, we say the star light is attenuated. Consequently, any emission we still measure from the UV light, reflects only a portion of the stars that have been formed. 

Now there are 2 choices, one can either try to correct for the dust attenuation or try to find the "missing" parts of the UV light. Let's start with the first, correction for dust. Here, again, you have several options. First, you can measure the slope of the galaxy spectrum in the UV and compare it to the slope that one would theoretically expect a spectrum to have. The difference between these two values is the amount by which the spectrum was attenuated (reddened). On the other hand you can fit theoretical galaxy spectra to the entire spectral energy distribution of the galaxy and gain a value of the amount of dust that reddened the galaxy from the best fit. However, there are several reasons why a galaxy's spectral energy distribution can have this shape and dust is only one of them. You can check this previous post to learn more about this issue. Finally, you can measure the strength of spectral lines, in particular hydrogen recombination lines such as Hydrogen alpha and Hydrogen beta, and forbidden oxygen lines ([OII] and [OIII]). These spectral emission lines occur because the most massive and hot stars heat and ionize the gas in their vicinity. When the ionization states change, light at particular wavelengths is emitted, which we then observe as emission lines. This line emission is also affected by dust attenuation.

If you went down the other route, you would need to find the missing light. Well, this UV light was absorbed by the dust around the newly formed stars. Consequently, the dust heats up and then re-radiates the light in the infrared portion of the electro-magnetic spectrum. Clearly, this measurement only provides you with the part of the UV light that was absorbed, so you measure the bit that you missed in the UV. So the combination of the uncorrected UV and IR star formation rate measurement gives you the total star formation rate in the galaxy. 

Unfortunately, the measurement of the IR emission also has disadvantages. For example, dust can also be heated somewhat by evolved, older stellar populations. Furthermore, dust emits the reprocessed light at a range of wavelengths depending on the size of the dust grains. In order to account for all emission a wide wavelength range in the IR needs to be covered and if the spectral energy distribution is too sparsely sampled in this region some portion of the emission might be missed. Moreover, at high redshift we are only able to detect the most luminous IR galaxies, but not those that are more like the Milky Way because they are too faint in the infrared.

I also mentioned at the beginning that X-ray and radio emission can be used to determine star formation rates. However, these are more uncertain as active galactic nuclei often dominate the emission at these wavelengths, hence what we measure does not all come from stars.

Astronomers try to combine various measurements for star formation rates and try to cross-correlate and calibrate the different ways to measure them. However, depending on the redshift of the galaxies in question, not all ways of measurement are possible or even accessible to us. In future posts on CANDELS science you will find out which ways CANDELS members use to get a handle on the star formation rates and what they have learnt from the measurements.

Galaxy Zoo meets CANDELS

As we discussed in this previous post, classifying a galaxy into morphological categories can tell us a lot about its structure. We often want to have classifications of large numbers of galaxies in order to  compare various properties (such as color, mass, star formation rates, etc.) with morphology. However, visual classifications can be very time consuming and classifying large samples (thousands of galaxies or more) can be a daunting prospect for any individual. In 2007 two astronomers, Kevin Schawinski and Chris Lintott, had a unique idea for how to deal with this problem - involve the general public in classifying galaxies - and Galaxy Zoo was born.

For the original Galaxy Zoo project, over one hundred thousand volunteers signed up to classify nearly one million galaxies from the Sloan Digital Sky Survey (SDSS). These volunteers determined whether each of the galaxies was a spiral or an elliptical and if it was a spiral whether it was rotating clockwise, counter-clockwise, or viewed edge on. Galaxy mergers and image artifacts were also options that the classifiers could select. Not only did these citizen scientists quickly take to classifying galaxies, they had fun and learned a lot about galaxies in the process. The Galaxy Zoo webpage hosts a forum where volunteers can post about interesting objects they find and discuss their classifications. One of the exciting aspects of having all of these galaxies looked at individually was the ability to identify rare and unique objects that had not been seen before, such as Hanny's Voowerp. These classifications have provided an incredible data set for Galaxy Zoo scientists and a number of publications have resulted from this tremendous effort.

The Galaxy Zoo project was further expanded with the start of Galaxy Zoo 2, which included a much more detailed look at a subset of galaxies, and Galaxy Zoo Hubble, which asks volunteers to classify galaxies imaged with the Hubble Space Telescope in a number of deep fields. Last month, Galaxy Zoo relaunched in its latest incarnation and now includes reprocessed SDSS images along with HST images from CANDELS. These new images have been discussed in great detail on the Galaxy Zoo blog. This is a unique and exciting project for CANDELS because now galaxies at high redshift with near-infrared data will be classified alongside SDSS galaxies by many people to produce a fantastic data set of classifications.

A sampling of colorized CANDELS galaxies that are in the newly relaunched Galaxy Zoo

We worked together closely with the Galaxy Zoo team to produce images for the website. Astronomers are used to analyzing images taken with a specific filter, or one very narrow portion of the spectrum. As such, these images are scientifically very useful, but we must look at images taken in different filters in order to study various galaxy properties. The beautiful color astronomical images that you are probably used to seeing combine several of these filters together. Since CANDELS images are taken in the near-infrared, which is not visible to the human eye, visible colors are assigned to the different near-infrared filters. These images are thus false-colored, but these colors represent real physical properties. The pictures above highlight what some of these CANDELS galaxies look like in color as they are being classified by volunteers.

Since the success of Galaxy Zoo, a number of other Citizen Science projects have begun. Collectively, these projects are a part of the Zooniverse and include things such as finding planets around other stars, studying the surface of the moon, and investigating the history of the Earth's climate. There are a number of interesting projects that anyone out there can contribute to. We hope you explore some of these while you are exploring Galaxy Zoo and looking at CANDELS galaxies!

Astronomer of the Month: Nimish Hathi

Each month we will highlight a member of the CANDELS team by presenting an interview introducing them and what it's like to be an astronomer. This month's Astronomer is Nimish Hathi.

Tell us a little about yourself!

My name is Nimish Hathi. I am a Postdoctoral Research Associate at Carnegie Observatories in Pasadena, CA. I am from India and have taken a long road to reach here. I did my Bachelor’s and Master’s in Physics/Electronics from Gujarat University in India. After my Masters, I went to Australia and attended the University of Queensland (UQ) in Brisbane for my second Masters, but this time in Astronomy. I spent a few months at the University of Western Australia in Perth before coming to the USA for my PhD. I completed my PhD at Arizona State University (ASU) in 2008.

What is your specific area of research? What is your role within the CANDELS team? 

My specific area of research is extragalactic astronomy. I study distant galaxies to understand their intrinsic properties and how these properties evolve with time. I am a co- investigator in the CANDELS team. I am involved in various working groups including galaxy morphologies, high redshift galaxies, and ultraviolet observations of lower redshift galaxies.

What made you want to become an astronomer? At what age did you know you were interested in astronomy? 

Challenge. Wow! While growing up in India, I did not have much exposure to astronomy and I got interested in astronomy only while taking postgraduate courses at UQ in Australia. So at a much older age than most other astronomers :-)

What obstacles have you encountered on your path to becoming an astronomer and how did you overcome them? 

As an international student, I/we face different kinds of obstacles. These could range from language and communication to social environment to living away from families (I visit my family every ~3 years) to immigration issues (e.g., the process to get visas for study, work or permanent residency can be time consuming and very frustrating) to financial restrictions, etc. How do I overcome those? Using the `hang in there’ motto. Keep going day-by-day and learn to deal with (most of) them.

Who has been your biggest scientific role model and why? 

No one in specific but I always look up to Indian scientists (e.g., Ramanujan, C.V. Raman, Chandrasekhar) who have risen from humble origins to scientific glory.

What is it like to be an astronomer? What is your favorite aspect? 

Special, something different from normal (profession). I like what I do but it is also little frustrating at times when I think about the future. My favorite aspect is to see the reaction of the people (specially in India) when I say I am an astronomer because still it is not the obvious or common profession in India. It is mostly one of awe.

 

What motivates you in your research? 

In day-to-day research we try to explore and understand unknown, new things and that keeps me going. Even if we don’t solve or understand everything, we learn and develop new important skills.

What is your favorite astronomical facility? (This could include telescopes or super computers, for example) 

Considering my very limited ground-based observing experience, I have to say the Magellan Telescopes in Chile.

Where do you see yourself in the future? What are your career aspirations? 

In the future, I would love to continue doing astronomy research, but I am also open to teaching and other job options. I will know soon when I start applying for a new job later this year.

If you could have any astronomy related wish, what would it be? 

Two wishes:-) 

I wish for better funding for current and future astronomy projects to continue our excellent research and make way for new discoveries.
 
I wish for more opportunities for permanent jobs to attract and retain young astronomers.

What is your favorite, most mind-boggling astronomy fact? 

The observational breakthroughs we have made in the last 10-20 years e.g., evidence for the big bang, existence of black holes, searching highest redshift galaxies, finding planets around other stars and many more.

Is there anything else you would like for the public to know about you or astronomy in general? 

I think the general public should know that astronomers not only gaze at the night sky with curiosity but they also develop techniques and technology which can be used in many other fields.

Enjoy the night sky :-)

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!