Undergraduates use SDSS Data to Discover the Densest Galaxies Known

Two undergraduates at San José State University have used public SDSS data to discover two galaxies that are the densest known. Similar to ordinary globular star clusters but a hundred to a thousand times brighter, the new systems have properties intermediate in size and luminosity between galaxies and star clusters.

The first system discovered by the investigators, M59-UCD3, has a width two hundred times smaller than our own Milky Way Galaxy and a stellar density 10,000 times larger than that in the neighborhood of the Sun. For an observer in the core of M59-UCD3, the night sky would be a dazzling display, lit up by a million stars. The stellar density of the second system, M85-HCC1, is higher still: about a million times that of the Solar neighborhood. Both systems belong to the new class of galaxies known as ultracompact dwarfs (UCDs).

The study, led by undergraduates Michael Sandoval and Richard Vo, used imaging data from the Sloan Digital Sky Survey, the Subaru Telescope, and Hubble Space Telescope, as well as spectroscopy from the Goodman Spectrograph on the Southern Astrophysical Research Telescope (SOAR), located on the Cerro Tololo Inter-American Observatory site. The National Optical Astronomy Observatory (NOAO) is a SOAR partner. The SOAR spectrum was used to show that M59-UCD3 is associated with a larger host galaxy, M59, and to measure the age and elemental abundances of the galaxy’s stars.

Two ultra-dense galaxies (insets) have been discovered orbiting larger host galaxies. The compact systems are thought to be the remnants of once normal galaxies that were swallowed by the host, a process that removed the fluffy outer parts of the systems, leaving the dense centers behind. Image credit: A. Romanowsky (SJSU), Subaru, Hubble Legacy Archive

Two ultra-dense galaxies (insets) have been discovered orbiting larger host galaxies. The compact systems are thought to be the remnants of once normal galaxies that were swallowed by the host, a process that removed the fluffy outer parts of the systems, leaving the dense centers behind. Image credit: A. Romanowsky (SJSU), Subaru, Hubble Legacy Archive

 

 

“Ultracompact stellar systems like these are easy to find once you know what to look for. However, they were overlooked for decades because no one imagined such objects existed: they were hiding in plain sight”, said Richard Vo. “When we discovered one UCD serendipitously, we realized there must be others, and we set out to find them.”

The students were motivated by the idea that all it takes to initiate a discovery is a good idea, archival data, and dedication. The last element was critical, because the students worked on the project on their own time. Aaron Romanowsky, the faculty mentor and coauthor on the study, explained, “The combination of these elements and the use of national facilities for follow up spectroscopy is a great way to engage undergraduates in frontline astronomical research, especially for teaching universities like San José State that lack large research budgets and their own astronomical facilities.”

The nature and origins of UCDs are mysterious – are they the remnant nuclei of tidally stripped dwarf galaxies, merged stellar super-clusters, or genuine compact dwarf galaxies formed in the smallest peaks of primordial dark matter fluctuations?

Michael Sandoval favors the tidally stripped hypothesis. “One of the best clues is that some UCDs host overweight supermassive black holes. This suggests that UCDs were originally much bigger galaxies with normal supermassive black holes, whose fluffy outer parts were stripped away, leaving their dense centers behind. This is plausible because the known UCDs are found near massive galaxies that could have done the stripping.”

An additional line of evidence is the high abundance of heavy elements such as iron in UCDs. Because large galaxies are more efficient factories to make these metals, a high metal content may indicate that the galaxy used to be much larger.

To test this hypothesis, the team will investigate the motions of stars in the center of M59-UCD3 to look for a supermassive black hole. They are also on the hunt for more UCDs, to understand how commonly they occur and how diverse they are.

Reference:

“Hiding in plain sight: record-breaking compact stellar systems in the Sloan Digital Sky Survey,” Michael A. Sandoval, Richard P. Vo, Aaron J. Romanowsky et al. 2015, Astrophysical Journal Letters, 808, L32. (Preprint: http://arxiv.org/abs/1506.08828)


 

This post is copied from a press release from the National Optical Astronomy Observatory.

NOAO is operated by Association of Universities for Research in Astronomy Inc. (AURA) under a cooperative agreement with the National Science Foundation.

The SDSS 2015 Collaboration Meeting

This past week was the 2015 SDSS Collaboration Meeting, held at the Instituto de Física Teórica IFT UAM-CSIC in Madrid, Spain (jointly organized by the Instituto de Física Teórica IFT UAM-CSIC and the Instituto de Astrofísica de Canarias).

Members of the SDSS Collaboration outside the IFT in Madrid earlier this week.

Members of the SDSS Collaboration outside the IFT in Madrid earlier this week.

You can read this news item (en Espanol) about the meeting: El “Sloan” continúa su exploración del Universo, or see this collection of Tweets by SDSS members during the meeting: Storify of #sdss15.

Spotlight on APOGEE: Jonathan Bird and the Formation of the Milky Way

The spotlight this month is on Jonathan Bird, the Vanderbilt Initiative for Data-Intensive Astrophysics Postdoc (VIDA) at Vanderbilt University. He is also the APOGEE-2 Science co-chair, for which he is responsible of “making sure that APOGEE-2 takes full advantage of the truly ground-breaking dataset the survey has produced.”

Jonathan is fascinated by the structure of the Milky Way Galaxy: Why is it shaped this way? What was it like in the past? And what will it be like in the future?

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Like many people, Jonathan developed a love for astronomy from an early age. His family home in the Santa Monica mountains offered beautiful views of the night sky.

But growing up, his real passion was basketball. He travelled extensively across the west and southwest for tournaments in high school, and was lucky enough to play college ‘ball when he arrived at Caltech — a team in need of little introduction.

Jonathan’s scientific interests have been widespread. Studying radio waves to investigate what determines the large-scale morphology of galaxies; using Cepheid variable stars to measure distances to galaxies; studying Asymptotic Giant Branch stars in order to understand their contribution to stellar synthesis models, a major component of galaxy models; and studying how a disk galaxy is assembled from smaller galaxies. Do you see a theme? In fact, Jonathan’s major interests can best be described by his PhD thesis title: “The Formation and Evolution of Disk Galaxies.” Jonathan’s goal is nothing less than understanding how the Milky Way came to be, how it evolved, and where it is going from here.

Perhaps that is why Jonathan fits in so well with the APOGEE team.

Let’s show one of Jonathan’s models from his 2013 paper on disk galaxy assembly. In the top left panel is shown the distribution of really old stars (11-12 billion years old) in a typical spiral galaxy. From left to right, and then continuing on the bottom, each panel shows the distribution of stars in a different age group (numbers in the bottom right of each panel show the age in billions of years). Notice that the “spiral” shape that we associate with spiral galaxies is found only among stars that are less than about 2 billion years old. As odd as this may seem, this is exactly what astronomers observe: the older stars are found across a large volume across the bulge and halo; whereas younger stars are predominantly found in the disk, where star formation is ongoing.

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How does this model hold up against the huge APOGEE-1 dataset? Pretty well, actually. For Jonathan, this is heartening — we have begun to piece together the massively complex stellar history of the Milky Way Galaxy, and we can do it with state-of-the-art telescopes and computer codes. You can follow more about what Jonathan is doing, along with the rest of the APOGEE-2 team, by following us on social media.

Social Media from the SDSS Collaborating Meeting in Madrid

This week many of us are at the Instituto de Física Teórica IFT UAM-CSIC in Madrid, Spain for our 2015 collaboration meeting (jointly organized by the Instituto de Física Teórica IFT UAM-CSIC and the Instituto de Astrofísica de Canarias).

The meeting hashtag is #sdss15.

Our twitter account @sdssurveys will be run by spokesperson, Jennifer Johnson this week. We’ll also be tweeting from survey accounts @mangasurvey (Karen Masters and Anne-Marie Weijmans), @APOGEEsurvey (by Jennifer Sobeck this week) and @eBOSSurvey (Britt Lundgren and Shirley Ho).

Join the conversation and find out what’s going on with the SDSSurveys right now.

Discovering Supernova in SDSS Galaxy Spectra

The post below was contributed by Dr. Or Graur, an assistant research scientist at New York University and research associate at the American Museum of Natural History. He recently led a paper based on supernovae detected in SDSS galaxy spectra (published in the Monthly Notices of the Royal Astronomical Society; the full text is available at: http://adsabs.harvard.edu/abs/2015MNRAS.450..905G).

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One of the great things about the SDSS is that it can be used in ways that its creators may never have envisioned. The SDSS collected ~800,000 galaxy spectra. As luck would have it, some of those galaxies happened to host supernovae, the explosions of stars, inside the area covered by the SDSS spectral fiber during the exposure time. These supernovae would then “contaminate” the galaxy spectra. In Graur & Maoz (2013), we developed a computer code that allowed us to identify such contaminated spectra and tweeze out the supernovae from the data. In Graur et al. (2015), we used this code to detect 91 Type Ia and 16 Type II supernovae.

 

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A galaxy+supernova model (blue) fits the SDSS spectrum (grey) much better than a galaxy-only model (green). The residual spectrum (lower panel, grey), after subtracting the galaxy component, is best-fit by a Type Ia supernova template (red).

With these samples, we measured the explosion rates of Type Ia and Type II supernovae as a function of various galaxy properties: stellar mass, star-formation rate, and specific star-formation rate. All of these properties were previously measured by the SDSS MPA-JHU Galspec pipeline.

 

In 2011, the Lick Observatory Supernova Search published a curious finding: the rates of all supernovae, normalized by the stellar mass of their host galaxies, declined with increasing stellar mass (instead of being independent of it; Li et al. 2011b). We confirmed this correlation, showed that the rates were also correlated with other galaxy properties, and demostrated that all these correlations could be explained by two simple models.

 

Type Ia supernovae, which are thought to be the explosions of carbon-oxygen white dwarfs, follow a delay-time distribution. Unlike massive stars, which explode rather quickly after they are born (millions of years, typically), Type Ia supernovae take their time – some explode soon after their white dwarfs are formed, while others blow up billions of years later. We showed that this delay-time distribution (best described as a declining power law with an index of -1), coupled with galaxy downsizing (i.e., older galaxies tend to be more massive than younger ones), explained not only the correlation between the rates and the galaxies’ stellar masses, but also their correlations with other galaxy properties.

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Type Ia supernova rates as a function of galaxy stellar mass

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Type Ia supernova rates as a function of specific star formation rate.

Simulated rates, based on a model combining galaxy downsizing and the delay-time distribution, are shown as a grey curve on both the above plots. This model is fit to the rates as a function of mass and then re-binned and plotted on the specific star formation rate plot, without further fitting.

For Type II supernovae, which explode promptly after star formation, the correlations are easier to explain; they are simply dependent on the current star-formation rates of the galaxies: the more efficient the galaxy is at producing stars, the more efficient it will be at producing Type II supernovae.

All of the supernova spectra from Graur & Maoz (2013) and Graur et al. (2015) are publicly available from the Weizmann Interactive Supernova data REPository (http://wiserep.weizmann.ac.il/). Please note that their continuua may be warped by our detection method (for details, see section 3 of Graur & Maoz 2013).

How SDSS Uses Light to Find Rocks in Space

It’s an exciting time in solar system exploration, with the Philae lander and Rosetta orbiter exploring Comet 67P Churyumov-Gerasimenko, sending back our most details view ever of a comet. On top of this the New Horizons Mission is approaching the dwarf planet Pluto, and will make its closest pass on 15th July 2015, sending back the highest resolution images of Pluto we have ever seen.

You might think that the Sloan Digital Sky Survey has nothing to say about rocks in space, but you’d be wrong. One of the possibly unexpected discoveries from our  imaging survey has been that of many hundreds of thousands of asteroids.

Because of the way the SDSS Camera Worked, asteroids show up in the SDSS imaging at different times (and therefore different places as they are moving across the sky) in the different filters. This makes them pop out as little strings of almost traffic light coloured dots. These have been popular finds by citizen scientists at Galaxy Zoo as well as identified by computer algorithms.

Asteroids (the three coloured dots) found near galaxies by citizen scientists at Galaxy Zoo.

Asteroids (the three coloured dots) found near galaxies by citizen scientists at Galaxy Zoo.

The below animation by Alex Parker shows the orbital motions of over 100,000 of the asteroids observed by the Sloan Digital Sky Survey (SDSS), with colors illustrating the compositional diversity measured by the SDSS five-color camera. The relative sizes of each asteroid are also illustrated.

 

All main-belt asteroids and Trojan asteroids with orbits known to high precision are shown. The animation has a timestep of 3 days. The fact that the composition of asteroids in the asteroid belt varys systematically is clearly visible, with green Vesta-family members in the inner belt fading through the blue C-class asteroids in the outer belt, and the deep red Trojan swarms beyond that.

Occasional diagonal slashes that appear in the animation are the SDSS survey beams.

The average orbital distances of Mercury, Venus, Earth, Mars, and Jupiter are illustrated with rings.

Colors represented with the same scheme as Parker et al. (2008). Concept and rendering by Alex H. Parker. Music: Tamxr by LJ Kruzer.


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. We’ve reached the halfway point here in June 2015! 

SDSS-IV Demographics Report Presented at Inclusive Astronomy

SDSS_demographics_logo The first conference on Inclusive Astronomy was held June 17-19, 2015 at Vanderbilt University in Nashville, TN.  The conference brought together professional astronomers, sociologists, education researchers, and experts on social justice, with the aim of collectively defining recommendations and actions to make the astronomical community more diverse and inclusive.  We are proud to note that the local organizing committee for Inclusive Astronomy included members of the SDSS-IV leadership: Keivan Stassun and Kelly Holley-Bockelmann of Vanderbilt University.

Britt Lundgren (UW-Madison), who co-Chaired last year’s Committee on the Participation of Women in the SDSS (CPWS) with Karen Kinemuchi (Apache Point Observatory), presented a poster on the 2014 SDSS-IV Demographics Report.  This report details the results of a voluntary survey of the SDSS-IV collaboration’s ~500 active members, and an analysis of the SDSS-IV membership and leadership in terms of gender, location, career stage, and minority status.   The report was recently accepted for publication in the August 2015 edition of the Publications of the Astronomical Society of the Pacific, and the full text of the report is currently publicly available on the arXiv.

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(Above: The basic demographic breakdown of the 250 SDSS-IV collaboration members who responded to the CPWS survey in 2014.)

Key findings from the 2014 SDSS-IV demographic report include:

  • 11% of survey respondents self-identified as a racial or ethnic minority at their current institution.
  • 25% of the SDSS-IV members are female.  This fraction is consistent with the American Astronomical Society membership, but higher than the reported fraction of female members in the International Astronomy Union (16%).
  • Large and approximately equal fractions of men (36%) and women (29%) self-identify as an SDSS-IV “leader,” perhaps due to active stakeholders being more likely to respond to a demographics survey.
  • When binned by academic age and career level, men and women in the SDSS-IV assume leadership roles at approximately equal rates, which increase steadily for both genders with increasing seniority.
  • At the highest level of SDSS-IV leadership, women disproportionately hold roles related to education and public outreach (E/PO; 3/4 female), as opposed to scientific or technical roles (2/16 female).

The efforts undertaken by the CPWS to address the demographics of the membership and leadership of SDSS-IV were very positively received at the Inclusive Astronomy conference. In addition, members of the leadership of LSST and DES in attendance voiced interest in producing similar reports from their collaborations, which will be among the largest in astronomy in coming years.   As a growing number of astronomers are participating in large international scientific collaborations, the CPWS is delighted to see other collaborations pursuing a similar accounting to ensure that these structures foster a healthy scientific climate that is both inclusive and diverse.

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(Top: The gender breakdown of the SDSS-IV collaboration members, as a function of years since receiving their final degree.  Bottom: The fraction of men and women who self-reported to hold positions of leadership within the SDSS-IV, as a function of years since their terminal degree.)

The 2014 SDSS-IV Demographics Report will provide a baseline for tracking changes within the makeup of the collaboration throughout the lifetime of the SDSS-IV.  This year’s CPWS, co-Chaired by Sara Lucatello (INAF) and Aleks Diamond-Stanic (UW-Madison), recently produced a follow-up survey for 2015, which broadened the demographics investigation to a larger range of diversity metrics (e.g., LGBT, disability, and partnership / family status).  The 2015 survey achieved a ~40% higher participation rate compared to 2014, with 352 members of the collaboration responding.

A summary of the initial results from the 2015 survey will be presented at the SDSS-IV Collaboration Meeting in Madrid later this month, so stay tuned!

The CPWS is currently comprised of the following members:
Alfonso Aragon-Salamanca (Nottingham)
Katia Cunha (Observatorio Nacional / MCTI)
Aleks Diamond-Stanic (UW Madison) Co-Chair
Bruce Gillespie (JHU)
Alex Hagen (PSU)
Amy Jones (MPA)
Karen Kinemuchi (APO)
Sara Lucatello (INAF) Co-Chair
Britt Lundgren (UW Madison)
Adam Myers (Univ. of Wyoming)
Alexandre Roman Lopes (ULS)
Gail Zasowski (JHU)

Outgoing members of the CPWS from 2014 include:
Jay Gallagher (UW Madison)
Shirley Ho (CMU)
Christy Tremonti (UW Madison)

SDSS Plates as Art in Nashville, Tennessee

Check out these cool art pieces made from SDSS spectroscopic plates!  Nashville based artist, Adrienne Outlaw, designed and built them and they will be exhibited in various locations at Vanderbilt University over the next year. The pictures show their first installation, just in time for the Inclusive Astronomy meeting that started yesterday. The concept design was done by Adrienne Outlaw in collaboration with Vanderbilt astronomers David Weintraub and Billy Teets, and the project was funded by Vanderbilt University’s Curb Creative Campus program.

If you want to learn more about what these plates are, and see them in other art installations please see this previous post on SDSS plates.

We love seeing images of SDSS plates around the world. Please send any you find to us via social media (you can find us on Facebook, Twitter and Google+), or email to outreach ‘at’ sdss.org.

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SDSS at the New York Hall of Science

A few months ago (at the end of March), SDSS Members spent a Saturday taking part in the Big Data Fest at the New York Hall of Science, in Queens, NY.

This event was aimed at helping people find out how data is relevant to their lives and featured interactive experiences focused on data literacy and data gathering and visualization.

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Chang Hahn and Yuqian Liu from NYU ready to go with the SDSS booth

Seven SDSS members in total helped out – six from NYU (Chang Hahn, Yuqian Liu, Nitya Mandyam Doddamane, Kilian Walsh, Ben Weaver, and Mike Blanton), along with Guang Yang who travelled up from Penn State University (PSU). This group ran one of about a dozen booths spread throughout the Hall of Science buildings in between the regular exhibits.

The SDSS booth contained an SDSS plate, along with a large-scale printout of the imaging for the part of the sky it was designed for. There was also a set of flash cards with images of galaxies on them, next to an invitation to try classifying them. Visitors were invited to take a card home with them if they wished. There were laptops running both Galaxy Zoo and the SDSS SkyServer. The SkyServer demo was set up to allow visitors to explore the data taken with the plate on display. Finally a monitor displayed a loop of videos about SDSS from the SDSS YouTube Channel.

Galaxy flashcards ready for classifying.

Galaxy flashcards ready for classifying.

The audience were made up of a mixture of children, teenagers and adults (including some who were very scientifically literate). The location in Queens meant that it was mostly NY area residents – with fewer tourists than Manhatten based museums attract.

Nitya Mandyam Doddamane and Yuqian Liu talks about SDSS with some visitors, while Chang Hahn is running a demo of Skyserver.

Nitya Mandyam Doddamane and Yuqian Liu talks about SDSS with some visitors, while Chang Hahn is running a demo of Skyserver.

This event at the NY Hall of Science is just one example of SDSS scientists around the world working to engage members of the public with our data. If you are running a similar event and might be interested in seeing if SDSS would be able to participate, please contact outreach ‘at’ sdss.org and we will try to connect you with your nearest SDSS institution.

APOGEE-South: Plate-Pluggers and Tripods – APOGEE-Sur: Conexión de Placas y Trípodes

Recently, a small group of astronomers from Chile has been visiting Apache Point Observatory. Their job will be to assist with operations at APOGEE-South, which is being built for the Irénée du Pont telescope at Las Campanas Observatory. Introducing: Christian Nitschelm, a faculty member at Universidad de Antofagasta; Andrés Almeida, a Masters student from Universidad Andrés Bello; and Jaime Vargas, Masters student at Universidad de La Serena.

Recientemente, un pequeño grupo de astrónomos de Chile ha estado visitando el Observatorio Apache Point (APO por sus siglas en Inglés). Su trabajo consistirá en ayudar con las operaciones en APOGEE-Sur, que se está construyendo para el telescopio Irénée du Pont en el Observatorio Las Campanas. Presentamos a: Christian Nitschelm, profesor en la Universidad de Antofagasta; Andrés Almeida, un estudiante de Maestría de la Universidad Andrés Bello; y Jaime Vargas, estudiante de Maestría de la Universidad de La Serena.

Jamie (left) Christian (center), and Andres (right), unplugging an APOGEE plate after observations. Jamie (a la izquierda), Christian (al centro), y Andrés (a la derecha), desconectando las fibras ópticas de una placa de APOGEE después de las observaciones.

Jamie (a la izquierda), Christian (al centro), y Andrés (a la derecha), desconectando una placa de APOGEE después de las observaciones.
Jamie (left) Christian (center), and Andres (right), unplugging an APOGEE plate after observations.

While at APO, Jamie, Christian, and Andres are learning a number of important skills that they will take back to Las Campanas Observatory. This includes plugging and unplugging plates:

Mientras tanto en el APO, Jamie, Christian y Andrés están aprendiendo una serie de técnicas importantes que llevarán al Observatorio Las Campanas. Esto incluye conectar y desconectar las placas:

Christian and Jamie seen here plugging fibers into a plug plate. Christian y Jaime se ven aquí conectando las fibras en una placa de conexión.

Christian y Jaime se ven aquí conectando las fibras ópticas en una placa de conexión.
Christian and Jamie seen here plugging fibers into a plug plate.

They are also learning to use the new Mock Up and Training Facility tripod, cartridge, and dolly (seen below). This setup will be sent down to Universidad de La Serena so that this crew can train future support staff.

También están aprendiendo a usar la maqueta y trípode de capacitación, el cartucho y carro (observados a continuación). Esta configuración se enviará a la Universidad de La Serena para que este equipo de trabajo pueda entrenar el personal de apoyo futuro.

Christian and Jamie swapping out a plug plate cartridge with the Mock Up and Training Facility tripod (the big steel frame), cartridge (the blue object suspended from the tripod) and dolly, which will be used to transport plug plates to and from the telescope. Christian y Jaime intercambiando el cartucho de la placa conexión con la maqueta y el trípode de capacitación (la estructura de acero grande), el cartucho (el objeto azul suspendido del trípode) y el carro, que será utilizado para transportar las placas de conexión hacia y desde el telescopio.

Christian y Jaime intercambiando el cartucho de la placa conexión con la maqueta y el trípode de capacitación (la estructura de acero grande), el cartucho (el objeto azul suspendido del trípode) y el carro, que será utilizado para transportar las placas de conexión hacia y desde el telescopio.
Christian and Jamie swapping out a plug plate cartridge with the Mock Up and Training Facility tripod (the big steel frame), cartridge (the blue object suspended from the tripod) and dolly, which will be used to transport plug plates to and from the telescope.

“Torquing” the plug plate slightly is a necessary skill so that it aligns with the field of curvature of the telescope. Using a ring around the plate (shown being attached below), the plate can be bent ever so slightly:

“Torcer” ligeramente la placa de conexión es una habilidad necesaria para alinear la placa con el campo de curvatura del telescopio. Usando un anillo alrededor de la placa (mas abajo se ve como se engancha), ésta se puede doblar ligeramente:

Christian and Andres attaching the bending ring around the plate. Christian y Andrés enganchan el anillo de flexión alrededor de la placa.

Christian y Andrés enganchan el anillo de flexión alrededor de la placa.
Christian and Andres attaching the bending ring around the plate.

And, of course, it is important to check your work. In this case, a computer is used to map the locations of fibers on the plate, ensuring that they will be on target when the plug plate is used on the telescope:

Y, por supuesto, es importante revisar su trabajo. En este caso, se utiliza un ordenador para mapear las ubicaciones de fibras en la placa, asegurando que van apuntar al objeto cuando la placa de conexión se use en el telescopio:

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Christian utiliza una computadora para medir el perfil de la placa de conexión después de que ha sido mapeada. Esto asegurará que la placa ha sido “torcida” correctamente.
Christian using a computer to measure the profile of the plug plate after it has been mapped. This will ensure that they have “torqued” the plate properly.

Jamie is enjoying his new skills set! Here, he is drawing an overlay on a plug plate to prepare it for plugging. ¡Jaime disfruta de sus nuevas habilidades! Aquí está dibujando una superposición en una placa de conexión para prepararla para la conexión.

¡Jaime disfruta de sus nuevas habilidades! Aquí está dibujando una superposición en una placa de conexión para prepararla para la conexión.
Jamie is enjoying his new skills set! Here, he is drawing an overlay on a plug plate to prepare it for plugging.

How SDSS Used Light to Make the Largest Ever Image of the Night Sky

The Sloan Digital Sky Survey imaged over 30% of the sky between the years of 1998-2008, creating the largest digital colour image of the sky ever taken. To view all of the SDSS imaging at once, would require 500,000 HD televisions (so it can be displayed at full resolution), and with more than a trillion pixels, this image dwarfs the 1.5 billion pixel image that NASA recently claimed was the biggest ever taken.

The SDSS Camera which took all of this imaging is now retired, and was collected by the Smithsonian Institution, to be packed away in a basement as an “artifact of scientific significance”.

The SDSS Camera in its current home - a basement of the Smithsonian Museum in Washington, D.C. Image Credit: Xavier Poultney, SDSS.

The SDSS Camera in its current home – a basement of the Smithsonian Museum in Washington, D.C. Image Credit: Xavier Poultney, SDSS.

The SDSS camera was made by arranging together an array of thirty, 2048×2048 pixel CCD chips. In the 1990s this was state-of-the-art, and even today a 126 Megapixel camera is nothing to sniff at (e.g the current state-of-the-art is DECam which has 62 CCDs and a total of 520 Megapixels).

The CCD chips in the SDSS camera were aligned in five columns, each covered by one of the five filters used to make the colour imaging (the u-, g-, r-, i- and z-bands, roughly corresponding to collecting light in the near-ultraviolet, green, red, near-infrared and a bit less near-infrared respectively).

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An illustration of the arrangement of the CCDs and filters on the camera. The filters from top to bottom are r, i, u, z and g-band. Image credit: SDSS.

This arrangement meant that the camera could take images continuously as the Earth rotated and moved it with respect to the sky overhead. SDSS images are therefore arranged in long stripes of constant Declination across the sky (the most famous being “Stripe 82” which was imaged many times). You can make out some of these stripes around the edges of the stitched together image (the “legs of the orange spider” below).

Orange Spider! This illustration shows the SDSS imaging on many scales. The picture in the top left shows the SDSS view of a small part of the sky, centered on the galaxy Messier 33 (M33). The middle and right top pictures are further zoom-ins on M33. The figure at the bottom is a map of the whole sky derived from the SDSS image. Visible in the map are the clusters and walls of galaxies that are the largest structures in the entire universe. Figure credit: M. Blanton and SDSS

All SDSS imaging is publicly available and can be explored online via the SDSS Skyserver. The Navigate Tool is especially fun as you can scroll around the entire image.

A much more technical description of the camera can be found in Gunn et al. (1998) and in the SDSS-I project book.


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 Plates for Education

Here at SDSS we’re working on a new educational initiative, where teachers and informal educators will be able to take back to their classroom their very own piece of SDSS history – an actual SDSS plate which was used to map a small patch of the night sky.

We have been developing a “Plate packet” to distribute to teachers and educators. This packet contains an SDSS plate, along with a custom made poster showing the SDSS image of the region of sky the plate was designed for, as well as some selected educational materials, and links to specially designed activities on SDSS Voyages.

Certificate handed out with each plate.

Certificate handed out with each plate.

On Saturday 30th May 2015, SDSS Members from the University of Washington handed out the first plates to a group of  teachers representing high schools from around the western Washington, USA. These teachers spent the day at the in Seattle discussing ideas for using the plates in their classrooms, as well as getting a tour of the machine shop, where all the SDSS plates are manufactured.

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“Hard at Work”: SDSS Member Oliver Fraser (pink shirt) shows some educators how to find the data from their plates and use it for classroom investigations. A plate poster can be seen on the board in back. Credit: Danielle Skinner

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“Yay Plates!”: some happy educators (and SDSS Member, Danielle Skinner in black) excited to be taking their very own SDSS plates back to their schools. Credit: Oliver Fraser.

The University of Washington is already planning more such workshops, and we look forward to expanding this program to other SDSS Member Institutions.


If you’re a teacher or educator reading this and interested to know how you can get your own SDSS plate, please contact the outreach representative at your nearest SDSS Institution, or email outreach ‘at’ sdss.org for assistance doing that. SDSS members interested in getting involved in this programme should join the EPO mailing list (details on the password protected collaboration wiki). 

David Schlegel Wins an Ernest Lawrence Award

Prof. David Schlegel of Lawrence Berkeley National Laboratory, the PI of the BOSS part of SDSS-III and a long time contributor to all areas of the Sloan Digital Sky Surveys was announced yesterday as one of the winners of the E.O. Lawrence Award.

David Schelegel, PI of BOSS, shows off a plug plate. Image credit: LBL

David Schelegel, PI of BOSS, shows off a plug plate. Image credit: LBL

The Ernest Orlando Lawrence Award was established in 1959 in honor of Ernest Lawrence, who invented the cyclotron (for which he won 1939 Nobel Laureate in physics). The Lawrence Award honors U.S. scientists and engineers, at mid-career, for exceptional contributions in research and development supporting the Department of Energy and its mission to advance the national, economic and energy security of the United States.

The citation for David’s award (for the High Energy Physics Category of the award) reads:

Honored for his exceptional leadership of major projects making the largest two-dimensional and three-dimensional maps of the universe, which have been used to map the expansion rate of the Universe to 10 billion light years and beyond. His fundamental technical contributions to high precision measurements of the expansion history of the Universe, and his massive galaxy redshift surveys to detect baryon acoustic oscillations, has helped ascertain the nature of Dark Energy, test General Relativity, and positively impact fundamental understanding of matter and energy in the universe.  These efforts have made precision cosmology one of the most important new tools of high-energy physics.

All of us at SDSS are delighted to wish David Schlegel many congratulations for this honor.

The SDSS Reverberation Mapping Project

The below post was contributed by Dr. Catherine Grier, a postdoctoral researcher at Penn State University (formerly a graduate student from Ohio State University, and the Director of the OSU Planetarium) who has led a recent paper based on results from the SDSS Reverberation Mapping Project (accepted for publication in the Astrophysical Journal; the full text is available at: arXiv:1503.030706 Screen Shot 2015-05-21 at 17.16.00 Supermassive black holes (SMBHs) are present in all massive galaxies and are thought to affect the formation and development of the galaxies themselves. Because of this, understanding SMBHs is important in understanding how galaxies are formed and evolve. Observations of quasars are key to understanding SMBHs and how they affect their host galaxies: Quasars are enormously powerful, observable at great distances, and can potentially regulate the growth of their galaxies through their winds, or outflows. We learn about these winds by observing broad absorption line features (BALs; see the diagram below) in quasar spectra that are created by high-speed winds launched from the quasar accretion disk. These winds are made of gas that blocks the light from the quasar and show up as BALs in the spectra of quasars.

Slide1

The CIV region of our target showing the CIV Broad Absorption Line (BAL) features investigated in our study.

These absorption features change throughout time, both in strength and in shape. Under the right conditions, we can use the details of the variability to learn about the density of the absorbing gas and the distance of the gas from the SMBH. This information can sometimes be used to determine if the outflow is powerful enough to affect the star formation in their host galaxy. Previous studies have found that BALs are variable on timescales of several years all the way down to timescales of 8-10 days; however, until now, no studies have reported variability on timescales shorter than 8-10 days. In our recent work, we report on very short-timescale (~1 day) BAL variability observed in a SDSS quasar. The spectra used in our study were taken as a part of the SDSS Reverberation Mapping (SDSS-RM) project using the BOSS spectrograph. We monitored 850 quasars with the BOSS spectrograph from January 2, 2014 through July 3, 2014, resulting in 32 observations over this period. The main goal of the SDSS-RM program is the investigation of the broad emission line regions of quasars, but the targets include a number of quasars hosting BALs and can be used for BAL studies too. During our observing campaign, the equivalent width, or strength, of the highest-velocity CIV BAL feature (see above diagram) changed by over a factor of 2. We did not observe similar variations in either the CIV broad emission line or the overall brightness of the quasar, and the shape of the BAL feature stayed roughly the same during the entire campaign. We observed significant changes in the strength of the BAL on timescales as low as 1.20 days in the quasar rest frame (see the graphs below). This is the shortest time frame ever reported over which significant variability in a BAL trough has been observed.

Slide2

Four different pairs of spectra between which the CIV BAL trough varies significantly.

The most likely cause of the variability is a change in the amount of ionized gas in the outflow. This could be caused by changes in the brightness of the quasar or the amount of energy reaching the absorbing gas for various other reasons. With our observations, we are unable to determine whether this outflow contributes significantly to feedback to the host galaxy, but we do not rule out the possibility. The key to observing this short-term variability was the high cadence of the SDSS-RM campaign, which allowed us to search for BAL variability on shorter timescales than previous studies. This program is still ongoing; we expect to receive more spectra of this target over the next few years with the eBOSS spectrograph, which could shed further light on this topic. The variability properties of this target are similar to those found in other quasars, suggesting that this short-term variability may be common. Further high-cadence spectroscopic campaigns targeting BAL quasars would allow us to learn more about BAL variability in quasars and better understand the possible contributions of BALs to feedback to their host galaxies.

Engineering Work for APOGEE-South – Trabajo de ingenieria en APOGEE-Sur

Telescopes at LCO

The du Pont 2.5m telescope on the middle-left, and the pair of Magellan 6.5m telescopes on the right.
El telescopio de 2.5m du Pont al centro hacia la izquierda y los dos telescopios de 6,5m, Magallanes, a la derecha.

A half-dozen SDSS scientists and engineers traveled to Las Campanas Observatory, Chile at the beginning of March to continue work on characterizing the 2.5m du Pont telescope performance in preparation for the first APOGEE-South hardware tests in August. This report is from the SDSS Operations Software Manager John Parejko, who was part of the run (and ended up involved in some hardware tests, against his better judgement!). Translated into Spanish by Verónica Motta, Associate Professor of Astronomy at Valparaiso University.

Las Campanas Observatory currently hosts three “large” telescopes (greater than 2 meters diameter), and a number of 1 meter diameter and smaller telescopes. The 2.5m du Pont telescope (in use since 1977) is a much older telescope than the 2.5m Sloan telescope at APO (in use since 1999), but it is at an excellent site, its optics are still very good–I heard them referred to as “superb” on several occasions–and it has a large field of view. With the assistance of the telescope’s owners–the Carnegie Institution of Washington–SDSS plans to help design improvements to the telescope drive systems so that we can run an APOGEE-South survey and fully sample the Milky Way’s bulge.

Una media docena de científicos e ingenieros del SDSS viajaron al Observatorio Las Campanas (Chile) a principios de marzo para continuar el trabajo de caracterización del rendimiento del telescopio de 2.5m du Pont en preparación para la primera prueba de hardware de APOGEE-Sur que se realizara en agosto. Este informe proviene del Director de Operaciones de Software del SDSS, John Parejko, que participó en la ejecución (y que terminó involucrado en algunas pruebas de hardware, en contra de su mejor juicio ! ). Traducción de Verónica Motta, profesor asociado de astronomía en la Universidad de Valparaíso.

El Observatorio Las Campanas actualmente alberga tres “grandes” telescopios (mayores de 2m de diámetro), y varios más pequeños de hasta 1m de diámetro. El telescopio de 2.5m du Pont (en uso desde 1977) es más antiguo que el telescopio de 2.5m Sloan en el Observatorio Apache Point (APO, en uso desde 1999), pero está en un lugar excelente, su óptica es todavía muy buena -he oído referirse a ella como “excelente” en varias ocasiones- y tiene un gran campo de visión. Con la ayuda de los propietarios del telescopio -la Institución Carnegie de Washington- el SDSS planea ayudar a mejorar el diseño de los sistemas de accionamiento del telescopio de manera que podemos realizar el relevamiento APOGEE-Sur y muestrear completamente el bulbo de la  Vía Láctea.

Paul and Nick looking at the rotator

Paul Harding and Nick MacDonald looking at the rotator.
Nick MacDonald y Paul Harding investigan las propiedades físicas del rotador del du Pont.

In order to determine what improvements the telescope requires, we have to make precise measurements of how different parts of the telescope move. From previous work, we found that the Right Ascension and Declination motors (equivalent to latitude and longitude projected onto the sky) probably don’t need much work. This trip, we measured the motion of the rotator and focus systems. Carnegie is in the process of completing their own upgrades to the telescope, and our measurements will help guide these changes.

Con el fin de determinar qué mejoras necesita el telescopio tenemos que hacer mediciones precisas de cómo se mueven las diferentes partes del telescopio. A partir de trabajos anteriores, encontramos que los motores de la Ascensión Recta y de la Declinación (equivalentes a la latitud y a la longitud proyectada sobre el cielo) probablemente no necesitan mucho trabajo. En este viaje medimos el movimiento del rotador y del sostema de enfoque. Carnegie se encuentra en el proceso de terminar sus propias mejoras al telescopio y nuestras medidas servirán de guía para estos cambios.

Author self portrait in a primary. You can see the reflection of the secondary mirror and its light baffles just above my head.

Author self portrait in a primary. You can see the reflection of the secondary mirror and its light baffles just above my head.
Autorretrato del autor en el primario, se puede ver el reflejo del espejo secundario y su luz que pasa justo por encima de mi cabeza.

To focus a telescope like this one, you move the secondary mirror. Even tiny changes in the position or tilt of the secondary can result in incorrect or uneven focus when you need a large field of view, as APOGEE will. As the du Pont is an older telescope, the system that moves the secondary mirror may not be as stable as APOGEE requires.

We first checked whether the mirror moved the exact amount each time it was commanded. We’ve found that the mirror motors need to be more repeatable: moving 500 “up” and then 500 “down” should return to exactly the same place, but it doesn’t. The Carnegie engineers are now working to improve the motors and control systems to fix this.

Para enfocar un telescopio como éste se mueve el espejo secundario. Incluso pequeños cambios en la posición o en la inclinación del secundario pueden resultar en un foco incorrecto o irregular en un gran campo de visión como el que utilizará APOGEE. Como el telescopio du Pont es viejo, el sistema que mueve el espejo secundario puede no ser tan estable como requiere APOGEE.

Primero revisamos si el espejo se movió la cantidad correcta cada vez que se le ordenó. Hemos encontrado que los motores del espejo tienen que ser más confiables: moverse 500 hacia “arriba” y después 500 hacia “abajo” debería regresarlo exactamente al mismo lugar, pero no es así. Los ingenieros de Carnegie están trabajando para mejorar la motores y los sistemas de control para solucionar este problema.

Author self portrait in the du Pont secondary, with my camera and our measuring target visible.

Author self portrait in the du Pont secondary, with my camera and our measuring target visible.
Autorretrato del autor en el secundario del du Pont, con mi cámara y nuestro objeto de medición visible.

To measure any shift or tilt in the secondary, we used a rather interesting system: a typical camera (the Panasonic G2 that I travel with for touristy photos; it took all the pictures shown in this post) with a long telephoto lens mounted on a moveable rail, taking pictures of the image in the secondary mirror of a “target” on the floor. We then took pictures with the camera and measured whether the target moved around: if it doesn’t move from image to image, we know the secondary is very stable against tilts and shifts during movement. We’re still analyzing the results of these tests, and will use them to detail what changes need to be made.

Para medir cualquier desplazamiento o inclinación en el secundario usamos un método interesante: una cámara típica (la Panasonic G2 con la que viajo para tomar fotos turísticas; la que tomó todas las imágenes que se muestran aquí) con un teleobjetivo largo montado en un carril móvil, toma fotos de la imagen en el espejo secundario de un “objetivo” en el suelo. Entonces tomamos fotos con la cámara y medimos si el objetivo se movió: si no se mueve de imagen a imagen, sabemos que el secundario es muy estable ante las inclinaciones y los cambios durante el movimiento. Todavía estamos analizando los resultados de estas pruebas y las usaremos para detallar los cambios deben hacerse.

Además de mi trabajo de ingeniería en el telescopio du Pont, tuve tiempo durante la noche para fotografiar el cielo austral. Este fue mi primer viaje al hemisferio sur y me aseguré de levantarme temprano al menos una mañana para ver las Nubes Mayor y Menor de Magallanes y toda la gloria de la Vía Láctea austral. Tuve que levantarme temprano para evitar la Luna casi llena, que disminuye la visibilidad. Sin duda tienen cielos espectaculares ahí abajo.

In addition to my engineering work on the du Pont telescope, I was able to take some time at night to photograph the southern sky. This was my first trip to the southern hemisphere, and I made sure to get up early at least one morning to see the Large and Small Magellanic Clouds and the full glory of the southern Milky Way. I had to get up early in order to avoid the nearly-full moon, which otherwise much diminished the view. They’ve certainly got some spectacular skies down there!

The southern hemisphere Milky Way and Large Magellanic Cloud, over the main LCO building.

La Vía Láctea y las Nubes Mayor y Menor de Magallanes Nube en el hemisferio austral, sobre el edificio principal del LCO.
The southern hemisphere Milky Way and Large Magellanic Cloud, over the main LCO building.

Pasé mis últimos días de este viaje en la ciudad de La Serena, reunido con la gente de la Universidad de La Serena (ULS) y reuniendo los resultados de las pruebas. Durante este tiempo, pude ver como la escuela de ingeniería ULS  maniobró la nueva máquina, marca Mazak CNC, con cuidado hasta su lugar en el taller de mecánica. Las instituciones chilenas han utilizado la colaboración SDSS/Chile para reforzar su infraestructura a través de subvenciones y varios acuerdos. En este caso, fueron capaces de comprar el modelo más avanzado de fresadora computarizada que planean utilizar para construir piezas para APOGEE-Sur.Tengo ganas de ver que pueden construir con ella!

I spent my last days of this trip in the city of La Serena, meeting with people at the University de La Serena (ULS) and collating results from the tests. During this time, I was on hand to watch as the ULS engineering school had a brand new Mazak CNC machine carefully maneuvered into place in their machine shop. Chilean institutions have used the SDSS/Chile collaboration to bolster their on-site infrastructure via grants and various agreements. In this case they were able to purchase a state-of-the- art computerized milling machine that they plan to use to construct parts for APOGEE-South. It will also provide engineering student training and experience, and allow the university to construct other cutting edge scientific equipment in the future.

I’m looking forward to see what they can build with it!

Happy Engineers standing in front of their just-delivered CNC machine. Ingenieros felices de pie frente a su recién entregada máquina CNC.

Ingenieros felices de pie frente a su recién entregada máquina CNC.
Happy Engineers standing in front of their just-delivered CNC machine.