Letter from the New Editor in Chief

Dear Readers of the SDSS Blog,

I am Zheng Zheng, a SDSS-IV postdoctoral research fellow at the National Astronomical Observatories, Chinese Academy of Sciences (NAOC). I will be your new Editor in Chief for the SDSS Blog for the next 6 months and I will try my best to work with other bloggers to make the blog posts more interesting and smooth.

I got my PhD at Johns Hopkins University and now I am a postdoctoral researcher working at the NAOC and partially at the Institute of Cosmology and Gravity (ICG) at the University of Portsmouth in the U.K. I am currently studying extra-galactic galaxies using the SDSS-IV MaNGA data. I am also interested/involved in MaNGA stellar library, APOGEE and eBOSS projects.

As you may have known, the SDSS is an internationally collaborated survey project and the member institutes come from all over the world. In the future, we will introduce more interesting SDSS related sciences/events from all over the world, including the U.S., Europe, East Asia, and South America. We are aiming to a post frequency of about 1 ‘long’ post (like the ones introducing science projects) per 1-2 weeks. We will also have ‘short’ posts reporting SDSS related events and/or short news.

Please do not hesitate to make comments and let us know your ideas about the blog posts. Your feedback is highly appreciated and we will try our best to post more articles according to your interests.

Sincerely,

Zheng Zheng

 

Zheng observing at Palomar

Tweep of the Week: Anne-Marie Weijmans

The MaNGA Lead Observer, and our Data Release Co-ordinator, Anne-Marie Weijmans will be spending some time at Apache Point Observatory Dec 8-17th and has agreed to take over the @sdssurveys Twitter account for the trip. We’re hoping for some tweets about pie (as well as observing).

MaNGA Lead Observer (Anne-Marie Weijmans) plugging IFUs into an SDSS plate. Credit: SDSS.

MaNGA Lead Observer (Anne-Marie Weijmans) plugging IFUs into an SDSS plate. Credit: SDSS.

 

Dr. Weijmans is a Lecturer (Assistant Prof. for our US readers) and Leverhulme Early Career Fellow based at the University of St Andrews in Scotland. Her research interests concentrate on the structure and evolution of early-type (i.e. visually smooth) galaxies using Integral Field Spectroscopy. Before joining MaNGA she was a member of the ATLAS-3D survey, which was one of the first surveys to use this technique on a sample of galaxies.

How SDSS Uses Light to Measure the Mass of Stars in Galaxies

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Galaxy NGC 3338 imaged by SDSS (the red stars to the right is in our own galaxy). Credit: SDSS

It might sound relatively simple – astronomers look at a galaxy, count the stars in it, and work out how much mass they contain, but in reality interpreting the total light from a galaxy as a mass of stars is fairly complex.

If all stars were the same mass and brightness, it would be easy, but stars come in all different brightnesses, colours and masses, with the lowest mass stars over 600 times smaller than the most massive.

Hertzsprung-Russel Diagram identifying many well known stars in the Milky Way galaxy. Credit: ESO

Hertzsprung-Russell (HR) Diagram, which shows the mass, colour, brightness and lifetimes of different types of stars. This version identifies many well known stars in the Milky Way galaxy. Credit: ESO

And it turns out that most of the light from a galaxy will come from just a small fraction of these stars (those in the upper left of the HR diagram). The most massive stars are so much brighter ounce for ounce than dimmer stars this makes estimating the total mass much more of a guessing game than astronomers would like (while they are 600 times more massive, they are over a million times brighter). So astronomers have to make assumptions about how many stars of low mass are hiding behind the light of their brighter siblings to make the total count.

One of the first astronomers to suggest trying to decode the light from galaxies in this way was Beatrice Tinsley. British born, raised in New Zealand, and working at Yale University in the USA, Dr. Tinsley had a much larger impact on extragalactic astronomy than her sadly shortened career would suggest (she died of cancer in 1981 aged just 40).

Stars of different masses have distinctive spectra (and colours), as first famously classified by Astronomer Annie Jump Cannon in the late 1890s into the OBAFGKM stellar sequence. O stars (at the top left of the HR diagram) are massive, hot, blue and with very strong emission lines, while M stars (at the lower right) are low mass, red and show absorption features from metallic lines in their atmospheres. With a best guess as to the relative abundance of different stars (something we call the “initial mass function“) a stellar population model can be constructed from individual stellar spectra or colours and fit to the total light from the galaxy. Example optical spectra of different types of stars are shown below (or see the APOGEE View of the IR Stellar Sequence)

Example optical spectra of different stellar types. Credit: NOAO/AURA/NSF

Example optical spectra of different stellar types. Credit: NOAO/AURA/NSF.

Using data from SDSS (and other surveys) astronomers use this methods to decode the galaxy light – in fact we can use either the total light observed through different filters in the SDSS imaging, to match the colours of the stars, or if we measure the spectrum of the galaxy we can fit a population of stars to this instead. While in principle the spectrum should give more information, in SDSS (at least before the MaNGA survey) we take spectra through a small fibre aperture (just 2-3″ across), so for nearby galaxies this misses most of the light (e.g. see below), and most galaxies have colour gradients (being redder in the middle than the outskirts), so the extrapolation can add quite a lot of error to the inferred mass.

NGC 3338 with the approximate SDSS fibre size overlaid (note this is an example of a very large galaxy imaged by SDSS). Credit: SDSS, KLM

NGC 3338 with the approximate SDSS fibre size (ie. the part of the galaxy for which we measured spectra) overlaid (note this is an example of a very large galaxy imaged by SDSS, and not representative of most galaxies). Credit: KLM, SDSS

 

Many astronomers prefer to use models based on the total light through different filters (at least for nearby galaxies). The five filters of the SDSS imaging are an excellent start for this, but extending into the UV with the GALEX survey, and IR with a survey like 2MASS or WISE adds even more information to make sure no stars are being missed. However, these fits are still a “best guess” and will still have error –  there is often more than one way to fit the galaxy light (e.g. model galaxies with certain combinations of ages and metallicities can have the same integrated colours), so there’s still typically up to 50% error in the inferred mass.

The SDSS camera filter throughput curves (from left to right ugriz). Credit: SDSS

The SDSS camera filter throughput curves (from left to right ugriz). Credit: SDSS

 

But with galaxies spanning more than 3 orders of magnitude in total mass (ie. the biggest galaxies have more than a 1000 times the stellar mass of the smallest) this is still good enough for many purposes. It gives us an idea of the total mass in stars in a galaxy, which (as you know from earlier post for IYL2015) is almost always way less than the total mass we estimate from looking at the dynamics (ie. the “gravitating mass”). And the properties of galaxies correlate extremely well with their stellar masses, so it’s a really useful thing to have even an estimate of.


This post by Karen Masters is part of the SDSS Celebration of the International Year of Light 2015, in which we aim to post an article a month in support of the celebration of light. 

P-MaNGA: Emission Lines Properties – Gas Ionisation and Chemical Abundances from Prototype Observations

(The following is a guest post by Francesco Belfiore, a PhD student at Cambridge University’s Kavli Institute for Cosmology, and summarizes his recent paper, which uses preliminary MaNGA data to map gas ionisation in several galaxies.)

Galaxies have long been considered island universes. Ordinarily separated by huge cosmological distances (of the order of millions of light years), most galaxies are not interacting in any visible way with their environment. However, modern theories of galaxy evolution claim otherwise. Starburst galaxies (galaxies which are experiencing a rate of formation of new stars much higher than normal) are known to expel large amounts of ionised (and possibly also neutral) gas towards the intergalactic voids. Supermassive black holes, which we believe to live in the centres of most galaxies, can also give rise to powerful outflows during periods of accretion (when the black hole has “switched on” and is feeding on the surrounding material). Some of these events are violent enough to totally strip a galaxy of its fuel: the gas. Without gas, a galaxy loses its ability to form new stars and becomes progressively older. In a sense, the galaxy has “died”.

This is not the whole story, however.

Continue reading

Integral Field Spectroscopy 101

As frequent readers know, the SDSS-IV-MaNGA survey plans to obtain spatially-resolved spectra of somewhere in the neighborhood of 10,000 galaxies using a technique called integral-field spectroscopy (or IFS). IFS essentially relies on placing an array of fiber-optic cables over an object of interest in the sky, and using the fiber-optics to pipe the light into a spectrograph, which produces the useful data by breaking up that light into its constituent wavelengths (an easy way you can do this at home is with a glass prism). The array of fibers is nicknamed a “bundle,” which is a pre-packaged grouping of fibers that we know the arrangement, and packaging the fibers allows more observational efficiency, since we don’t have to re-position the telescope to make a measurement of the same galaxy at a slightly different point.

However, the specific design of the fiber bundles is an important problem. Continue reading

How SDSS Uses Mysterious “Missing Light” to Map the Interstellar Medium

This post by Gail Zasowski is part of the SDSS Celebration of the International Year of Light 2015, in which we aim to post an article a month in support of the celebration of light. 


 

It is increasingly rare for modern astronomers to work on “old” puzzles — that is, older than they are, or especially older than their advisors are. The last several decades have seen a huge advancement in our understanding of the Universe — we learned that stars evolve over time in predictable ways, that the Milky Way is one distinct galaxy among many, and that the Universe itself is expanding and even accelerating in size “outwards”. Very often, the questions that astronomers work on now are new questions that arise as other problems are answered, or as we build new telescopes and discover things that we didn’t even know we didn’t know about.

But there is one outstanding puzzle that has famously resisted an answer for nearly a century now. This mystery concerns a peculiar pattern of missing light arising from interstellar material — that is, from the giant clouds of dust and gas that lie in the vast distances between stars. These clouds contain atoms and molecules of all the elements that make up the stars and the planets and us — hydrogen, carbon, oxygen, and so on. They are 10^19 (that’s 10 000 000 000 000 000 000) times less dense than the air we breathe, but they are so huge that they contain enough atoms to add up to nearly 15% of the mass of the Galaxy! (Baryonic mass, of course — dark matter is a different story.) And now the SDSS has made some unique contributions to understanding the mystery in these clouds’ missing light.

Figure 1: The inner part of the Milky Way Galaxy, with numerous stars intermixed with giant clouds of interstellar gas and dust.  Image credit: Serge Brunier.

Figure 1: The inner part of the Milky Way Galaxy, with numerous stars intermixed with giant clouds of interstellar gas and dust. Image credit: Serge Brunier.

 

Some of the atoms and molecules in interstellar clouds emit light, like visible light or radio waves, that we can see with telescopes. But others don’t emit much light, and the only way we know they’re there is when they absorb some of the light of stars when the light passes through one of these interstellar clouds. Helpfully, each kind of atom or molecule absorbs only specific wavelengths of light, and we can measure these wavelengths in a laboratory to learn what the pattern is for each element or molecule. So when we look at the spectrum of one of these stars seen through a cloud, and we notice that some of the star’s light is missing, we can use the patterns of absorbed wavelengths to figure out what kind of atoms or molecules are in the cloud. For example, this is how we know that the clouds have elements like calcium and potassium in them1.

Okay, on to SDSS and the mysterious missing light! Way back in the late 1910s, astronomers started noticing some absorption patterns in their spectra that were very puzzling. They didn’t act like the patterns from atoms in the stars themselves, so they had to come from interstellar material. And they appeared in the spectra of stars all over the sky, so the material had to be something that was common. But they couldn’t figure out what the particles were! The patterns didn’t match those of anything we knew existed in interstellar clouds, or even anything we had measured in a laboratory.

Fast-forward nine decades, and the situation has progressed a bit, but not as much as one might expect. We now know of almost 500 separate absorption “features” (that is, wavelengths at which light is being absorbed by something), up from the original 2 discovered in the 1910s (Figure 2). We call all of these features “DIBs”, which stands for “Diffuse Interstellar Bands”2. We have determined that the DIBs are more consistent with being caused by molecules than by single atoms, and many people have theories as to which molecules those are. But it was just this year, in 2015, that scientists were first able to show conclusively that a particular molecule — the fullerene ion C60+ — is responsible for a particular DIB (actually, for four of them). The rest remain up for grabs!

Figure 2: The 400 strongest known DIBs.  The y-axis shows the typical fraction of background light absorbed when there is enough interstellar dust to absorb almost 60% of the total visible light.

Figure 2: The 400 strongest known DIBs. The y-axis shows the typical fraction of background light absorbed when there is enough interstellar dust to absorb almost 60% of the total visible light.

So where does SDSS come in? Well, proving that certain molecules produce certain DIBs requires a lot of equipment and a molecular spectroscopy laboratory, and that’s not really something SDSS is set up to do. But there’s another related puzzle — how are the molecules that produce the DIBs (whatever they are) distributed throughout the Milky Way? This is an important question, because the big molecules that are most likely to cause the DIBs are the kinds of molecules that contain a lot of the Galaxy’s carbon, which has an impact on things like the chemistry of newly formed planets. But because DIBs are generally only studied in small samples of stars very close to the Sun3, we didn’t have a good understanding of what the molecules were doing elsewhere in the Galaxy.

One group of SDSSers (led by Ting-Wen Lan, a graduate student at Johns Hopkins) tackled this issue by looking for the DIBs’ absorption signatures in optical SDSS spectra of other galaxies and quasars, seen through the Milky Way’s interstellar material. They had to be careful, because the galaxies’ and quasars’ spectra have absorption lines from their own stars and gas clouds, so identifying the weak features from the foreground Milky Way gas can be tricky. But the SDSS provides the biggest dataset available to look for DIBs: the team had so many spectra from SDSS-I, -II, and -III (almost 500,000 of them) that they could add many spectra together to boost the signal, and then map the DIB absorption strength on the sky (see the left side of Figure 3). Because they detected about 20 DIB features in each signal-boosted spectrum, they could also measure how each DIB behaves a little differently with respect to other interstellar gases, like hydrogen or carbon monoxide (Lan et al. 2015). This tells us that there isn’t one single molecule that can explain all of the DIBs!

However, the SDSS optical dataset doesn’t include any sources in the disk or inner parts of the Milky Way. This is because the interstellar material, which is concentrated in these parts of the Milky Way, is made up of not only gas particles but also dust grains (think of tiny soot particles). These dust grains block starlight, and block it much more than the DIB molecules do, especially at optical wavelengths. (Look back at the picture of the inner Milky Way in Figure 1.) So it is very hard to see any stars, galaxies, or quasars to use as “background” sources in which to look for DIBs.

Figure 3: Left: The strength of DIB absorption seen in optical wavelengths from SDSS background galaxies and quasars (Lan et al. 2015) and in infrared wavelengths with APOGEE (Zasowski et al. 2015).  Click HERE for an interactive version of this map!  Right: The motion of the APOGEE DIB molecules with respect to the Sun.  Image credit: T. W. Lan and G. Zasowski.  (HERE=http://www.pha.jhu.edu/~tlan/dibs-map.html)

Figure 3: Left: The strength of DIB absorption seen in optical wavelengths from SDSS background galaxies and quasars (Lan et al. 2015) and in infrared wavelengths with APOGEE (Zasowski et al. 2015). Click HERE for an interactive version of this map! Right: The motion of the APOGEE DIB molecules with respect to the Sun. Image credit: T. W. Lan and G. Zasowski.

And this is where APOGEE steps in. APOGEE is unique in the SDSS set of instruments because it measures light at infrared wavelengths. This kind of light is invisible to the human eye (we can perceive some infrared wavelengths ourselves, though we call it “heat”!), but it is very efficient at passing through some materials, including the interstellar dust that blocks visible light (Figure 4). This means that APOGEE is a great tool for measuring starlight — and the bits of it that get absorbed by the DIBs — very far from the Sun in the disk and bulge, where most of the stars and interstellar material are!

Figure 4: Looking at things with optical and with infrared light can lead to very different results!  On top, a plastic bag is opaque to visible light, but it is translucent to infrared light from the man's hand.  On the bottom, a similar effect occurs in an interstellar cloud, seen with visible light (left), like our eyes, and infrared light (right), like APOGEE.  Image credits: NASA/IPAC and ESO.  See more optical/IR comparisons HERE.  (HERE=http://coolcosmos.ipac.caltech.edu/cosmic_kids/learn_ir/)

Figure 4: Looking at things with optical and with infrared light can lead to very different results! On top, a plastic bag is opaque to visible light, but it is translucent to infrared light from the man’s hand. On the bottom, a similar effect occurs in an interstellar cloud, seen with visible light (left), like our eyes, and infrared light (right), like APOGEE. Image credits: NASA/IPAC and ESO. See more optical/IR comparisons HERE.

So I (Gail Zasowski, a postdoc at Johns Hopkins) led a second group of SDSSers who focused on a single, particularly strong DIB feature that APOGEE could detect. My team measured this feature in front of about 70,000 stars in the APOGEE dataset (Zasowski et al. 2015a). Because most of these stars lie in the dustiest parts of the Milky Way, we were able to fill in the parts of the DIB absorption map that Ting-Wen’s group couldn’t reach with optical data (left panel of Figure 3). We also found that, unlike many of the DIB features at visible wavelengths, this infrared DIB does not disappear in cold, dense interstellar clouds. This behavior means that the APOGEE DIB can be used to measure the approximate amount of interstellar material between us and a background star, including the amount of interstellar dust that blocks so much of the starlight.

Even more excitingly, my team is able to use the DIB features we detect to measure the speed at which the clouds of DIB molecules are moving with respect to the Sun. We can tell that the molecules are generally rotating with the Galactic disk in the same way that hydrogen and other major interstellar components do (right panel of Figure 3).  Since most DIB studies in the past have looked at stars relatively close to the Sun, this is the first time this dynamical behavior has been observed in any sort of large scale way.

My group even found evidence for DIB molecules flowing in the gas surrounding the beautiful Red Square Nebula (Figure 5). This detection may help us identify likely candidates for the molecule itself (Zasowski et al. 2015b).

Figure 5:  The Red Square Nebula.  Image Credit: P. Tuthill.

Figure 5: The Red Square Nebula. Image Credit: P. Tuthill.

Over the last hundred years, astronomers have learned that there is a large reservoir of unidentified, complex organic molecules in the interstellar medium, seen only in the mysterious signatures they leave in the light of stars shining through them. The SDSS has given us the ability to use these DIB features — even without knowing exactly what causes them! — to map the distribution and velocities of these molecules in the big spaces between the stars.


 

1 Some elements are also traced through their light emission, instead of light absorption. This has to do with the more complicated physics that happens in clouds with different densities and temperatures. For more information, check out http://www.ipac.caltech.edu/outreach/Edu/Spectra/spec.html, or search for “astronomical spectroscopy” online.

2This term refers to three facts about these features. Many of the features at optical wavelengths appear strongest in “diffuse” interstellar clouds, as opposed to very cold dense clouds with atoms packed more closely together (still very far apart by Earth standards, though). The “interstellar” part distinguishes them from absorption features coming from the atmospheres of stars. “Band” is used to indicate that the majority of the features appear broad in the spectrum of a background star — much broader than the narrow absorption lines coming from the star itself.

3This is because bright stars that are close to the Sun tend to have very few absorption lines coming from their own atmospheres, so it’s much easier to detect interstellar absorption lines.


This post by Gail Zasowski is part of the SDSS Celebration of the International Year of Light 2015, in which we aim to post an article a month in support of the celebration of light. 

SDSS Survey Operations Software Developer

The below is the text of a job advert looking for a software developer to work on the software we use to run our surveys.

For full details please visit the Job Advert.

SDSS Survey Operations Software Developer

The Department of Astronomy at the University of Virginia (UVa) invites applications for a Survey Operations Software Developer to work directly with the Sloan Digital Sky Survey (SDSS-IV).  The SDSS-IV Survey, operating over the 2014-2020 period, consists of three, distinct astrophysical projects: eBOSS, which obtains precision measurements of key cosmological parameters; APOGEE, which performs a high-resolution, near-infrared spectroscopic survey of the Milky Way Galaxy; and MaNGA, which generates spatially resolved spectroscopic maps of individual galaxies.  SDSS-IV conducts observations from both a Northern Hemisphere Site at Apache Point Observatory (APO) in New Mexico and a Southern Hemisphere Site at Las Campanas Observatory (LCO) in Chile.  UVa is a full institutional participant in SDSS-IV as well as a member of the Astrophysical Research Consortium (ARC, which owns and manages APO).

The SDSS operations software contains the high-level data commands that execute survey observations, including telescope and instrument control, telescope guiding, back end frameworks, data storage and flow, observer GUIs and web applications. In the main, the Survey Operations Software Developer will maintain, document and improve the suite of SDSS operations software.  The successful applicant will interact with a variety of SDSS personnel (e.g., observers and other site staff, project scientists) and will coordinate the efforts of project software developers.  The specific responsibilities of the Survey Operations Software Developer include:

  • Ensuring that the SDSS observing system meets performance and reliability requirements.
  • Improving SDSS observing software and procedures and document the various improvements accordingly.
  • Testing, installing, and debugging newly developed software.
  • Tracking and resolving issues reported by the trouble-ticket system.
  • Responding to problems that occur during nightly observing.
  • Anticipating and planning for future survey operational needs.
  • Contributing to the LCO/APOGEE-2 operations software development.

A Master’s degree in Physics, Astronomy or a related field is required; a Ph.D. is preferred.  Applicants should possess proficiency in Python as well as knowledge of Unix Operating Systems.  The applicant should be substantially familiar with IDL and other programing languages in order to support SDSS legacy code. The initial appointment will be for one year.  Note, however, it is expected that the position should continue through the duration of SDSS-IV (mid-2020; contingent upon performance and available funding).  The hire will be done at the Research Associate level or higher, commensurate with experience.  Personal research time may also be available for the successful applicant.  Though the position will be based in Charlottesville, Virginia, travel to the APO and LCO sites will be expected.

For details on how to apply please see the full Job Advert.  Review of applications is planned to commence 1st December 2015.

The University of Virginia is an equal opportunity/affirmative action employer. Women and members of underrepresented groups are strongly encouraged to apply.  SDSS is also committed to work to increase the diversity of collaboration members.

Spotlight on APOGEE: Gail Zasowski and Cosmic Dust

Meet Gail Zasowski — postdoctoral research fellow at Johns Hopkins University and one of the people behind creating the APOGEE-2 target sample. She earned her PhD at the University of Virginia in 2012 and was then awarded an NSF fellowship at The Ohio State University. She is now a postdoctoral research fellow at Johns Hopkins University. One of Gail’s research interests is the interstellar medium (ISM), and this blog post will introduce how she has used APOGEE to study dust and molecules in the ISM.

fan_mountain_cropped

Gail grew up in western New York and in Knoxville, Tennessee. In college, she double majored in physics and Latin. As a PhD candidate at UVa, she studied dusty young protostars, the distribution of dust in the Milky Way Galaxy, and stellar populations in open clusters, that is, determining their ages and distances.

One of her explorations with APOGEE data has been in a unique approach to studying diffuse interstellar bands (DIBs), which are absorption features seen in many optical and near-infrared spectra that are believed to be due to large molecules in the ISM. These features are found in nearly every APOGEE spectrum, because the ISM lies between the Earth and every star that we study. The exact nature of these large molecules has been a question for some decades. In one paper, Gail and her collaborators demonstrated that DIBs trace the known distribution of dust throughout the ISM (check out the cool graphic below, from a press release), and can be used to independently verify the large-scale structure of the Milky Way Galaxy.

Gail successfully mapped the strength of DIB features in APOGEE spectra across the Milky Way Galaxy, and used them to show that DIBs trace the distribution of cosmic dust in between stars, but can also be used to trace large scale structure as well.

Gail successfully mapped the strength of DIB features in APOGEE spectra across the Milky Way Galaxy, and used them to show that DIBs trace the distribution of cosmic dust in between stars, but can also be used to trace large scale structure as well. The high latitude data comes from Ting-Wen Lan at JHU.

Even cooler, Gail also found evidence for circumstellar (that is, surrounding a particular star) DIBs in the dusty protoplanetary nebula MWC 922. This is an exciting result: it shows that the molecules that create DIBs are not merely confined to the ISM, but can be found in dusty environments around stars, too. And this is important because one of the unanswered questions about large molecules in space is how they are formed. Placing them around stars, and perhaps eventually showing that they originate around stars before being put in the ISM, would be a major step forward in cosmic dust studies.

Now Gail wants to apply her knowledge of surveys like APOGEE to create models of galaxies that can be used to understand resolved stellar populations (like the Milky Way’s) and unresolved stellar populations (such as the faint light that can be seen in more distant galaxies). This ties in well with several SDSS surveys, which study individual stars (e.g., APOGEE and SEGUE) and entire distant galaxies (e.g., MaNGA. Such a comparison should shed light on those parts of the Milky Way that are not well understood (such as its location in the Tully-Fisher plane, which can be used to determine a galaxy’s mass), as well as tell us about specific properties concerning other galaxies that show similarity to the Milky Way.

Do you think that all work and no play has made Gail a dull astronomer? Not at all! She was a founding member of the Dark Skies, Bright Kids! program at the University of Virginia, which seeks to provide science education in an informal setting to rural, underserved school children in central Virginia. She runs an annual space camp in Columbus, Ohio, that is aimed at middle school students. She is part of the Committee for the Participation of Women in SDSS, which seeks to promote gender balance and an inclusive environment within the collaboration, whose findings were published recently and can be read about on this blog. She also supports LGBTQ initiatives within her own department at JHU.

Gail’s wide-ranging interests, and those of her colleagues, have made a positive impact on the APOGEE survey — not only is it useful for stellar populations studies (which is what it is designed for), but it can also be used to study cosmic dust!

What is MaNGA (in one sentence)?

MaNGAlogo5small

 

Some months ago, members of the MaNGA (Mapping Nearby Galaxies at Apache point observatory) survey (part of SDSS-IV) were asked to suggest ideas for a suitable taglines/catchphrase which would describe the survey in one sentence. This idea was that this would go on promotional materials SDSS-IV would take to the American Astronomical Society Meeting, and also the main SDSS website.

The working favourite to that point had been “the galaxy survey for people who love galaxies”, but we wanted something which described the scientific goals of the survey more precisely.

In the word of MaNGA PI, Kevin Bundy this request resulted in an “outpouring of creative, collective genius” (a phrase which Kevin suggested might itself be the appropriate one to describe the MaNGA team).

Here are some of the ideas the team came up with, catagorised by Kevin:

Ideas which reference The 3rd Dimension

  1. .. Now in 3D!
  2. Sloan goes 3D
  3. Sloan Galaxies in three dimensions
  4. Galaxies in 3D
  5. A new dimension in galaxy surveys
10 000 (nearby) galaxies mapped in 3D
  6. A multi-dimensional view of galaxies
  7. Galaxies in 3D by the thousands
  8. Thousands of local galaxies in 3D
  9. Ten thousand Galaxies. Three dimensions

Inspirational ideas

  1. To boldly go where no other Galaxy survey has gone before.
  2. Unravelling the galaxy avatar
  3. Ten thousand mysteries unfold

Direct (or descriptive) ideas:

  1. Census of local galaxies
  2. MaNGA: Deciphering galaxies pixel-by-pixel
  3. Observing the dynamical structures and composition of galaxies to unravel their evolutionary histories
  4. Galaxy birth, assembly, growth and ‘death’
  5. Galaxies Beyond the Central Fiber
  6. Spatially resolved spectroscopy of 10,000 nearby galaxies

Ideas Inspired by Biological Analogies

  1. Galaxy dissection
  2. Galaxies under the microscope
  3. Exploring the life cycle of galaxies
  4. Anatomising galaxies dead and alive
  5. Dissecting galaxies in their dark matter haloes

Humorous suggestions

  1. Galaxies do the full monty
  2. Everything you wanted to know about galaxies, and in 3D
  3. Experience galaxies in 3D, without the glasses

Clever/cultural references

  1. Taking spectra of the spectrum of galaxies
  2. Galaxies in 3D! It’s over 9000!!
  3. 10K3D
  4. How galaxies tick

The final decision was made to go with “Mapping the inner workings of thousands of nearby galaxies” for our website, and we have a banner which says “The 3D Lives of Galaxies”, although we also really like the creative idea of making an API to return all of these randomly.

MaNGA - Mapping the inner workings of thousands of nearby galaxies

 

Many thanks to: Jeff Newman, Bob Nichol, Kyle Westfall, Surhud More, Karen Masters, Aaron Dutton, Claire Lackner, Mike Merrifield, Daniel Thomas, Eric Emsellem, Carles Badenes, Anne-Marie Weijmans, Brian Cherinka, Demitri Muna, Brett Andrews, Christy Tremonti and Kevin Bundy for contributing ideas.

 

IYL2015 Post: SDSS Plates (in Retirement!)

As part of Dresdner Lichtjahr 2015 [Dresden Year of Light 2015], you can now see a previously-used SDSS plate on display at Technische Sammlungen der Stadt Dresden, a museum located in a former Dresden factory. The exhibit will run through June of 2016, and has some really awesome demonstrations of how light propagates, and how much today’s technology depends on light.  Technische_SammlungenThe SDSS plate (below, designated plate 4385) is suspended above a table illustrating principles of how light propagates, what we can do with light of different wavelengths, and a demonstration of fiber optics. If you’re curious why our telescope might need need a metal plate, read this previous post.

Technische_Sammlungen2Used SDSS plates are available for educational purposes by schools, museums, astronomy clubs, and other educational & community organizations. Just contact someone at your nearest SDSS member institution to get started!

Technische_Sammlungen3Elsewhere in the exhibit and the museum, you can find a working infrared camera (selfie-compatible!), a very challenging puzzle involving prisms and laser light, and other neat activities suitable for children of all ages.

While you’re in Dresden, make sure to also stop by the Mathematische-Physikalische Salon [Royal Cabinet of Mathematical and Physical Instruments], at the Zwinger Palace in the center of Dresden, to have a look at old telescopes, clocks, and surveying tools. Of special interest to telescope enthusiasts are two very early reflector telescopes (i.e., telescopes that use a mirror to focus the incoming light, rather than lenses). You can also see them online in a panoramic view (upstairs in “Instruments of Enlightenment”).

 


This post is part of the SDSS Celebration of the International Year of Light 2015, in which we aim to post an article a month in support of the celebration of light. 

The Apache Point Observatory Galactic Evolution Experiment (APOGEE)

The following is a synopsis of the new overview paper describing the APOGEE survey. You can find the full paper here.

The first thing to show you about this paper is its authors list. Check out how many contributors there are to this survey:

TitleAuthors

This, together with its length (50 pages) and number of figures (38!!) may give you some idea of the huge scope of the project. To help us sift through it, here is the executive summary, from the APOGEE Principal Investigator, Steven Majewski:

“This paper gives a broad overview of the motivations, design and execution of the APOGEE survey — a synopsis of how the survey was structured and why.”

This isn’t just a technical overview of the survey, however. Says Majewski:

“The most fun part of this new overview paper — a part for which the entire APOGEE team can be justly proud — is the summary of what the project managed to accomplish in such a relatively short amount of time.”

Here are some examples of what he means:

  • 13 technical papers on subjects like spectrograph design, target selection, data reduction, stellar parameter determination, and collaborations with other surveys
  • Uses of time series spectral data for projects as diverse as spectroscopic binary characterization and circumstellar variations around hot stars
  • Detailed maps of stellar radial velocities and metallicities across the Milky Way

It should be mentioned that APOGEE was made possible by a unique 300-fiber-fed, high resolution spectrograph working in the infrared H-band. Hence, thirteen technical papers, while a seemingly large number, were all necessary because APOGEE truly broke ground in a number of ways, both scientific and technical. The actual construction was accomplished by the APOGEE instrument team led by John Wilson (Instrument Scientist) and Fred Hearty (Project Manager).

The detailed maps mentioned in the last bullet deserve a couple of images — they’re too cool not to show. In Figure 24 from the paper, the velocities of stars relative to the Sun are shown against an artist’s impression of the Milky Way Galaxy. Notice how there are clear areas where stars are approaching us, co-moving with us, and moving away from us:

Fig24_RVs

Figure 25 is a similar plot, but showing instead the chemical composition (metal content with respect to hydrogen) in stars across the same survey area. Check out the clear gradient from low-metallicity stars near the edge of the Milky Way’s disk to high-metallicity stars near the Galactic Center:

Fig25_MH

The general trends shown here are not new; instead, it is APOGEE’s unprecedented detail that makes it the biggest kid on the Galactic evolution block. To put APOGEE into context for us, here is Ricardo Schiavon, the APOGEE Survey Scientist, to sum it up:

“APOGEE has, for the first time, provided a homogeneous database of high quality, high resolution infrared spectra for 150,000 stars, which together offer a rigorously systematic spectroscopic census of our home galaxy. Because of it’s unique infrared sensitivity and ability to punch through the blankets of obscuring Galactic dust in its most crowded regions, APOGEE is unveiling the chemical and kinematical properties of stars in parts of the Milky Way never before probed in such exquisite detail. It is a groundbreaking experiment.”

To put it more bluntly: no one has ever done an infrared survey of Milky Way stars in this way.

APOGEE-South: Guiding with the du Pont Telescope

An important aspect of telescope control is to make sure that the telescope is tracking the sky at the right rate. Major motors ensure that this is done approximately, by matching the telescope’s position to the Earth’s rotation. But fine-tuning is usually required, and the practice of making these fine-tuned changes is known as “guiding”.

Recently, the SDSS Engineering Crew at Las Campanas Observatory in Chile made a tremendous step forward by figuring out how to guide with the du Pont telescope. APOGEE-South will rely on guiding in order to stay on target while it is making observations. Here is a picture of the guiding camera on the telescope, along with a number of people who worked to make this happen:

The guiding camera is seen at the bottom of the du Pont Telescope at Las Campanas Observatory in Chile. Fred Hearty (head, bottom left), Paul Harding (left, red jacket), John Wilson (behind Paul), French Leger (behind the guiding camera), Juan Trujillo (to right of guiding camera), and John Parejko (who took the picture) are responsible for the recent progress.

The guiding camera is seen at the bottom of the du Pont Telescope at Las Campanas Observatory in Chile. Fred Hearty (head, bottom left), Paul Harding (left, red jacket), John Wilson (behind Paul), French Leger (behind the guiding camera), Juan Trujillo (to right of guiding camera), and John Parejko (who took the picture) are responsible for the recent progress.

John Parejko also created a 30-second movie showing what guiding data look like. The bright “dots” in the video are stars that are being kept in their place by means of the guiding operations.

How SDSS Uses Light to Study the Most Abundant Element in the Universe

When we spread out the light from a source into a rainbow, we can reveal information about its chemical makeup. This is how we understand the spectral signatures that reveal that stars have different temperatures. But to learn about the objects that we study in space, whether they be stars, interstellar gas, or galaxies, we first have to know something about the chemical properties of the elements that make up these objects. And one of these elements is, by far, the most important to study: Hydrogen.

Why is hydrogen the most important element to study in astronomy? Primarily because it is the most abundant. If you count the number of hydrogen atoms in all of space (stars, gas, and galaxies), it can be shown that nine out of ten atoms in space are hydrogen. The second-most abundant is helium, which makes up almost one out of ten atoms in space, and every other element is present in only trace amounts — which is not to say that they are unimportant! But in this post, we are going to focus on the big one.

 

The Hydrogen atom, consisting of a single proton as the nucleus orbited by a single electron.

The Hydrogen atom, consisting of a single proton as the nucleus orbited by a single electron.

Hydrogen is also the simplest element on the Periodic Table, as the above diagram shows — one lone proton being orbited by one electron. And like all elements, hydrogen is able to absorb and emit light of certain wavelengths. If the electron is hanging out in the ground state (the n=1 state), it can absorb photons that will shimmy it to the n=2, n=3, n=4, etc. state (and there are an infinite number of these states). Likewise, if the electron begins in the n=2 state, then the atom can absorb photons of light to push it into the n=3, n=4, n=5, etc. state.

When a hydrogen atom is in one of these “excited” states (i.e., n 1), it also has the opportunity to emit a photon and travel back down to a lower energy level. The photons absorbed have the same wavelengths as the photons emitted, so that they always appear in the same place in a spectrum. In the following illustration, the first four energy levels of the hydrogen atom are shown. Three commonly-studied transitions between different energy levels are named, along with their absorption/emission wavelengths in units of Ångströms (= 10-10 m). The colors of the line are the approximate colors that they might appear to your eye — with the exception of the Lyman-α transition, which emits in the ultraviolet and is therefore invisible to the human eye.

An illustration of the four lowest energy levels of the Hydrogen atom, and commonly studied transitions between these energy levels.

An illustration of the four lowest energy levels of the Hydrogen atom, and commonly studied transitions between these energy levels.

 

When studying spectra from space, it is common to study either absorption spectra (spectra with lines that show that atoms are absorbing photons) or emission spectra (spectra with lines that show that atoms are emitting photons). The absorption process is the most common when studying stellar spectra. And for many stars, it is the hydrogen lines that gives us a first indication about the physical properties of the stars. Here, for instance, is the spectrum of an A-type star, i.e., one with strong Hydrogen absorption features:

Spectrum of an A0 star exhibits strong Hydrogen absorption lines where indicated. Other, smaller absorption lines are due to calcium, magnesium, and sodium absorption. This spectrum is taken from the Science Archive Server -- check it out!

Spectrum of an A0 star exhibits strong Hydrogen absorption lines where indicated. Other, smaller absorption lines are due to calcium, magnesium, and sodium absorption. This spectrum is taken from the Science Archive Server — check it out!

Galaxies, which are large conglomerations of stars, can also show hydrogen absorption features. But many galaxies, like spiral galaxies or else irregular galaxies with ongoing star formation, actually produce strong emission features. This is because the hydrogen gas that exists between the stars in these galaxies is heated by the stars, so that individual atoms are excited to higher energy levels. A great example is the spectrum of the irregular galaxy NGC 6052, shown below:

Spectrum of the irregular galaxy NGC 6052, with hydrogen emission lines labeled.

Spectrum of the irregular galaxy NGC 6052, with hydrogen emission lines labeled.

 

You might have noticed in this galaxy spectrum that these hydrogen emission lines appear to sit on top of what look like hydrogen absorption features. The absorption features, as mentioned above, come from the stars in the galaxy, whereas the emission features come from the gas between the stars.

There is other cool stuff that hydrogen can teach us. One of the coolest is called the Lyman-α Forest, which can be used to tell us how much hydrogen gas exists on large scales between galaxies.


This post is part of the SDSS Celebration of the International Year of Light 2015, in which we aim to post an article a month about how SDSS uses light in our mission to study the Universe. 

SDSS at the 29th General Assembly of the International Astronomical Union

The 29th General Assembly of the International Astronomical Union is due to start on Monday 3rd August 2015 in Honululu, Hawaii. These meetings happen every 3 years and are the biggest single conference in astronomy. This is your guide to all things SDSS related at IAU2015.

Thanks to generous support from the central project office, SDSS Education will be particularly well represented at IAU2015. SDSS Educational Consultant (Kate Meredith) and Director of EPO (Karen Masters) will be attending to run workshops on how to use SDSS data for education.

Screen Shot 2015-07-31 at 14.44.32

This half day splinter session on Monday 10th August will give astronomers and educators (including, but very definitely not limited to members of the SDSS collaboration) a chance to participate in a hands on workshop exploring voyages.sdss.org, a new educator focused resource designed to enable the use of real data from the Sloan Digital Sky Surveys in the classroom. Participants will have the opportunity to contribute their own experiences using data in the classroom into new guided journeys through Voyages for specific educational levels and/or suggest new content based on exploration of SDSS data. The schedule of the workshop is as follows:

Workshop Schedule (Drop-in Welcome), Monday 10th August 2015 in Room 327, Hawaii Convention Center.

  • 8.30am: Welcome
  • 8.40am: Mapping the Universe with SDSS (Karen Masters)
  • 9.15am: Introduction to SDSS Voyages (Kate Meredith)
  • 10.00am: COFFEE BREAK
  • 10.30am: Matching content to a curriculum (Kate Meredith)
  • 10.50am: Hands on exploration of voyages.sdss.org
  • 12.00pm: Lunch/work time
  • 1.00pm: SDSS Plates and how to get one (Karen Masters)
  • 1.30pm: SDSS Plate resources online (Kate Meredith)
  • 2.00pm: END

The SDSS EPO group will run a similar workshop, but this time especially for High School Teachers as part of the Galileo Teacher Training Program, happening at the IfA, Honululu on 8th/9th August. One lucky Hawaii based teacher attending this training will be able to take an SDSS Plug Plate back to their school for use in lessons.

The SDSS EPO group will be active participants in Focus Meeting 19: Communicating Astronomy with the Public in the Big Data Era. As part of that, SDSS Director of EPO, Karen Masters will lead a discussion on what Researchers would like to Improve in Communication Initiatives. The outcome of this meeting is intended to be a Playbook on Communicating Astronomy with the Public in the Big Data Era.

There are also of course numerous science results from SDSS data being presented at the meeting. Thanks to the open data policy of SDSS many of these results are from scientists who have never been part of the SDSS Collaboration. Here is a summary of all the posters and talks at IA2015 which can obviously linked to SDSS data or projects.

Week 1 Posters:

FM16p.13. White dwarf+main sequence binaries identified from SDSS DR10, Lifang Li

FM19p.16. Galaxy Zoo: Science and Public Engagement Hand in Hand
Karen Masters; Chris Lintott; Julie Feldt; Bill Keel; Ramin Skibba

FM19p.17. SDSS Plate Packets – From Artifact to Teaching Tool
Kate K. Meredith; Karen Masters; Britt Lundgren; Oliver Fraser; Nick MacDonald

FM19p.18. SkyServer Voyages Website – Using Big Data to Explore Astronomy Concepts in Formal Education Settings
Kate K. Meredith; Karen Masters; Jordan Raddick; Britt Lundgren

S315p.193. High Resolution Molecular Gas and Star Formation in the Strongly Lensed z~2 Galaxy SDSS J0901+1814
Chelsea Sharon; Andrew Baker; Amitpal Tagore; Jesus Rivera; Charles Keeton; Dieter Lutz; Linda Tacconi; David Wilner; Alice Shapley

S315p.235. Detecting HII Regions in Z=0.1 Galaxies with Multi-Band SDSS Data
Chris Richardson; Anthony Crider; Benjamin Kaiser

Week 2 Posters:

DJp.2.15. Extreme Red Quasars in SDSS-BOSS
Fred Hamann; Nadia Zakamska; Isabelle Paris; Hanna Herbst; Carolin Villforth; Rachael Alexandroff; Nicholas Ross; Jenny Greene; Michael Strauss

DJp.2.19. Environmental dependence of AGN activity in the SDSS main galaxy sample
Minbae Kim; Youn-Young Choi; Sungsoo S. Kim

DJp.2.24. Exploring large-scale environment of SDSS DR7 quasars at 0.46Hyunmi Song; Changbom Park

FM14p.06. The link between galaxy mergers and single/double AGN: a statistical prospective from the SDSS
Xin Liu

P2.096. An efficient collaborative approach to quasars’ photometric redshift estimation based on SDSS and UKIDSS databases
Bo Han; Yanxia Zhang; Yongheng Zhao

S319p.01. SDSS J012247.34+121624, one of the most dramatic BALQSOs at redshift of 4.75 discovered by the Lijiang 2.4m Telescope
Weimin Yi

S320p.10. White dwarf + main sequence binaries identified from the data release of the Sloan Digital Sky Survey (SDSS)
Lifang Li
FM7p.06. Stellar mass of elliptical galaxies in the Sloan Digital Sky Survey
Chen-Hung Chen; Chung-Ming Ko

S319p.05. Variability of 188 broad absorption lines QSOs from the Sloan Digital Sky Survey
Weihao Bian

S319p.251. Redshift-Space Enhancement of Line-of-Sight Baryon Acoustic Oscillations in the Sloan Digital Sky Survey Main-Galaxy Sample
Haijun Tian; Mark C. Neyrinck; Tamas Budavari; AlEXANDER SZALAY

Talks/Sessions:

 

Wed 5th
12.00pm: FM4.1.05 Hot evolved stars in massive galaxies
Claire Le Cras

Mon 10th
Voyage to Education with the Sloan Digital Sky Survey
Organizer(s): Karen Masters (University of Portsmouth), Kate Meredith (Yerkes)
8:30 AM – 2:00 PM; Room 327, Hawaii Convention Center

Thurs 13th
11.35am: FM7.5.05 Age derivation from UV absorption indices and the effect of the UV upturn.
Claire Le Cras

Mon 10th
Voyage to Education with the Sloan Digital Sky Survey
Organizer(s): Karen Masters (University of Portsmouth), Kate Meredith (Yerkes)
8:30 AM – 2:00 PM; Room 327, Hawaii Convention Center

2.30pm: S319.10.03. Extreme Red Quasars in SDSS-BOSS
Fred Hamann; Nadia Zakamska; Isabelle Paris; Hanna Herbst; Carolin Villforth; Rachael Alexandroff; Nicholas Ross; Jenny Greene; Michael Strauss

Fri 14th
10.55am FM17.7.02. Synergies of CoRoT asteroseismology and APOGEE spectroscopy — Applications to Galactic Archaeology
Friedrich Anders; Cristina Chiappini; Thaíse S. Rodrigues; Andrea Miglio; Josefina Montalbàn; Benoit Mosser; Leo Girardi; Marica Valentini; Matthias Steinmetz

12.00pm S319.12.06. Redshift evolution of massive galaxies from SDSS-III/BOSS
Daniel Thomas


 

If you are attending the IAU2015 we hope you have a great time, and we’ll see you on Social Media Karen Masters will be tweeting as @sdssurveys on #iau2015.

How SDSS Splits Light into a Rainbow for Science

All of the Sloan Digital Sky Surveys currently active (APOGEE, eBOSS, MaNGA, Spider and TDSS) are spectroscopic surveys. A spectroscope is a scientific instrument, which splits light into a rainbow (or spectrum) in order to make precise measurements of the amount of light of different colours (or wavelengths). To date the SDSS collaborations have used three different spectroscopes (the SDSS, BOSS and APOGEE instruments) to measure the rainbow of light from millions of stars and galaxies in our mission to map the Universe. Below is an image of one of these spectrographs.

 

boss_spectrograph

The BOSS Spectrograph. In centre the instrument is shown with optical fibres plugged into it. The diagrams at the side show the path of the light through the instrument after it passes down the fibre. Different parts are labelled.This instrument you have made has many similarities to the BOSS spectroscope shown above.

It is possible to make your own spectroscope using simple household materials and use it to measure the spectra of common light sources.  Here are instructions to build an SDSS CD Spectropscope. This instrument you can make has many similarities to the BOSS spectroscope shown above. For example:

  1. You will construct a slit through which the light will pass. In the diagram of the BOSS spectroscope this is labeled “slit-head”, and the light from the optical fibres is collected, “collimated” (i.e. lined up) and passes though it.
  2. You will use an old CD to make a grating (the BOSS spectroscope has 4 gratings; 2 on each side, and sandwiched between prisms to make a “grism”). A typical CD is made with 625 lines per mm. The the BOSS spectrograph has 520 and 400 lines/mm for the blue and red sides respectively.

Your spectroscope will be sensitive to all visible light. In the BOSS spectroscope a “dichroic” is used to split the light into red and blue before passing it through the gratings. A dichroic has a special property that it is reflective to blue light, while red light passes through it. This means the light can be spread out more, and special cameras can be used to detect light from near ultraviolet, right across the visible rainbow to the near infrared.

Instead of a camera you will use your eye (or you could try using a camera lined up with the viewing window). In the BOSS spectroscope there are four cameras (two for blue and two for red light) each kept specially cold in a “dewer”.

When the light passes through the slit it gets spread out a little bit, and then when it passes through the CD, the very fine slits in it (the diffraction grating) spread it out more. Different colours are spread out (or “dispersed”) by different amounts. The angle of dispersion is set by both the wavelength (colour) of the light, and the line spacing on the diffraction grating. The below image illustrates this (compared to refraction which can also create spectra; this is the physics which creates natural rainbows from refraction in raindrops). The diffraction angle increases with wavelength (and decreases with the line spacing).

Comparison of the spectra obtained from a diffraction grating by diffraction (1), and a prism by refraction (2). Longer wavelengths (red) are diffracted more, but refracted less than shorter wavelengths (violet).Credit: Wikimedia

Comparison of the spectra obtained from a diffraction grating by diffraction (1), and a prism by refraction (2). Longer wavelengths (red) are diffracted more, but refracted less than shorter wavelengths (violet).Credit: Wikimedia

Here are some examples of the kind of spectra you should be able to take with your CD spectroscope.

Example spectra through a CD spectroscope. Credit: CoolStuff Newsletter

Example spectra through a CD spectroscope. Credit: CoolStuff Newsletter

To make precise measurements we don’t tend to look at a pretty image of a rainbow, but instead make a graph which shows the brightness as a function of the wavelength (colour). An example of this is shown below which is a typical spectrum of a galaxy shown at five different distances (or redshifts).

redshift

The spectrum of a galaxy shown at five different distances (or redshifts), z=(0.0, 0.05, 0.10, 0.15, 0.20) corresponding to distances of (6, 12, 18 and 21 hundred million light years). Credit: SDSS Skyserver

If you do make an SDSS CD Spectroscope please take a picture (either of it or through it) and share it with us on Twitter or Facebook.


 

This post is part of the SDSS Celebration of the International Year of Light 2015, in which we aim to post an article a month about how SDSS uses light in our mission to study the Universe.