SDSS Collaboration Meeting 2016: Madison, Wisconsin, USA

At the end of June 2016, over 150 members of the SDSS collaboration met for workshops, talks, discussions, and fun by the lake at the University of Wisconsin, Madison. The week began with a two-day APOGEE workshop on Saturday and Sunday. On Sunday, the APOGEEans were joined in Madison by the FAST/REU bootcamp and the Plate workshop for teachers and scientists.

2016 SDSS collaboration meeting photograph. The happy attendees gathered by the beautiful lake. If you were there and not in this picture, you were probably getting coffee.

2016 SDSS collaboration meeting photograph. The happy attendees gathered by the beautiful lake. If you were there and not in this picture, you were probably getting coffee.

The FAST/REU students were getting up to speed really quickly on how to work with our data. The REU students are undergraduates who will be working on a science project over the summer, while the FAST students are graduate students in longer term teams with SDSS as we seek to help raise the participation of under-represented minorities.

On Monday-Wednesday, the meeting focused on discussions of SDSS-IV science, including many exciting results from the MaNGA survey, which is releasing its first data in Data Release 13. The APOGEE-2 survey present maps of the composition of stars across the Galaxy, characterizing the trends with position. The eBOSS survey showed the first results for large-scale structure of the Universe based on the 2014-2016 observations (very fast turn-around!). Quasars were also a big topic of conversation, as SDSS is now studying their evolution in detail. We are interested both in how they change over a few years time and mapping how they “grow” the supermassive black holes over billions of years. Results discussed that have been highlighted by SDSS in press releases/blog posts include the shutting off of star formation in galaxies by Edmond Cheng , additional examples of “changing look quasars” by Jessie Runnoe and the discovery that brown dwarfs could be quite common around certain types of stars by Nick Troup.

Poster for Daniel Eisenstein's public talk

Poster for Daniel Eisenstein’s public talk

We saw ways that other galaxies could “quench” their star formation in the presentation by Francesco Belfiore and could study the history of star formation in our Galaxy thanks to age maps by Melissa Ness. Apparently our galaxy has some similarities to other spiral galaxies! We tweeted a whole bunch about about the science results and will Storify some of our most popular tweets soon.

On Tuesday night, we had the collaboration meeting banquet, where we honored Dan Long, longtime Sloanie who worked at Apache Point Observatory for over 20 years, including as Chief Telescope Engineer for the Sloan Foundation Telescope. He is retiring next year and, as the email from Jim Gunn put it, “we will miss him more than I can say.” In addition to spoken tributes, we also showed of a movie of some of Dan’s greatest hits and well-wishes from the many other Sloanies. We will be posting that to youtube soon, so stay tuned.

The SDSS collaboration is big and includes people from many career stages, institutions, and cultures. We take the opportunity of these meetings to discuss how the collaboration is working and what we can do better. There was a thoughtful and thought-provoking discussion of how to improve the climate in SDSS and how to establish a “Code of Conduct” that will work to ensure that all are treated with respect.

This meeting also featured our first public talk by Daniel Eisenstein, talking about using the disturbances that sound waves left in the gas of the early Universe to trace the shape, past, and future of the Universe. He’s been working with SDSS data on this subject for over 10 years, so is a leading expert in this amazing result. The April 2016 edition of Sky and Telescope featured the article “Mapping the Universe’s Ancient Sound Waves” written by Daniel. The “Beyond the Pages” addition by the editors is also wonderful.

We had our most ambitious meeting ever for education and public outreach. The Plate Workshop on how to use an SDSS plate to introduce your class to the science of SDSS had a number of educators from across the US attending, looking pretty happy when they got their picture taken.

Educators from the Plate Workshop, organized by Kate Meredith (bottom right) and Karen Masters (who is probably taking the picture)

Educators from the Plate Workshop, organized by Kate Meredith (bottom right) and Karen Masters (who is probably taking the picture)

The Sunday workshop was followed on Monday and Tuesday by educators attending science talks, working with SDSS scientists on education and public outreach ideas, and doing an “EPO Hack Day” to create new activities for Voyages, SDSS’s website for how to use our data for education for K-12 students.

Thanks to the University of Wisconsin, especially the head of the Local Organizing Committee, Christy Tremonti, for hosting such a lovely meeting and we look forward to seeing everyone at the next meeting next summer.

SDSS Celebrates Leaders Inducted into the National Academy of Sciences

This year, we are pleased that two scientists related to the SDSS collaboration have been recognized for their wide contributions to astronomical research.

Professor Meg Urry, of Yale University, has served on the Advisory Committee for SDSS-III and SDSS-IV. Her research focuses of supermassive black holes, and she is known, among other things, for her work that demonstrates Active Galactic Nuclei are a common phase in galaxy evolution.

Dr. Meg Urry of Yale University

Dr. Meg Urry of Yale University

Professor Timothy Heckman, of John Hopkins University, has also served on the Advisory Committee for SDSS, as well as being an Astrophysical Research Consortium Board member from 1995 to 2000. His research touches upon the ways that supermassive black holes effect their host galaxies.

Dr. Timothy Heckman, Johns Hopkins University

Dr. Timothy Heckman, Johns Hopkins University

Congratulations to both Timothy and Meg on their achievements!

Red Geysers in MaNGA: New Evidence for AGN Maintenance Mode Feedback

(This is a guest post by Edmond Cheung at the Kavli IPMU)

While there have been many recent studies addressing how galaxies shut off, or quench, their star formation, an equally interesting yet relatively unstudied question is how these quenched galaxies remain quenched. This is interesting because these quiescent galaxies often contain gas (from stellar mass loss or mergers) that—if left unimpeded—should cool and form stars. But since we know that quiescent galaxies have not formed a significant amount of stars since they’ve been quenched, there must be something that prevents this gas from cooling.

In the new study by Cheung et al. 2016, Nature, 533, 504, this ‘something’ has been found. Using the ongoing SDSS IV MaNGA survey, which takes resolved spectroscopy for 10,000 nearby galaxies, Cheung et al. discovered a new class of quiescent galaxies—dubbed “red geysers”—that hosts outflowing winds powerful enough to heat ambient gas and suppress future star formation. These winds are manifested in bisymmetric emission features (in H-alpha, [OII], and other strong lines) and are likely powered by their weakly-accreting supermassive black holes.

To highlight the key characteristics of this class, Cheung et al. focus on a prototypical red geyser, which they nicknamed “Akira”—a reference to the critically-acclaimed manga comic of the same name, and in homage to the MaNGA survey and the lead author’s current institute in Japan (Kavli IPMU). Akira is undergoing a minor interaction with another galaxy, which they’ve nicknamed “Tetsuo”—another character in the same manga comic as Akira; the SDSS image of the interaction is shown in panel a of the figure below, which is reproduced from the Cheung et al. 2016. According to merger simulations, Tetsuo is depositing cool gas into Akira, which is detected in redshifted Na D absorption (panels d and e). The expected star-formation from this cool gas, however, is absent: Cheung et al. find that the measured star-formation rate of Akira is much lower than what is expected given the amount of cold gas present. Thus something is prohibiting star formation in Akira—what is it?

The image and diagnostic diagrams of  "Akira", a prototypical red geyser.

The images and diagnostic diagrams of “Akira”, a prototypical red geyser. 

Inspecting the ionized gas properties of Akira, Cheung et al. find an interesting bisymmetric emission pattern in H-alpha and other strong emission lines (panel c). These emission patterns roughly align with the ionized gas velocity gradient (panel h), suggestive of an outflow. To prove that the ionized gas is in an outflowing wind instead of in a rotating disk, Cheung et al. had to disprove the latter case. Using the stellar dynamics of Akira (panels f and g), they obtain a tight constraint on its gravitational potential, from which they are able to predict the ionized gas kinematics in the case of a regularly rotating disk. They find that the observed ionized gas kinematics are significantly higher than the predicted ionized gas kinematics (panel j), indicating that the ionized gas is not under the influence of gravity alone.

Ruling out the disk interpretation, Cheung et al. developed a qualitative wind model that reproduces many of the features of the data, including the ionized gas velocity field and the ionized gas velocity dispersion field. They theorize that this outflowing wind is likely powered by the weakly-accreting supermassive black hole at the center of Akira, which is detected as a central radio point source in the FIRST survey and in followup Jansky VLA observations. They calculate that the energetic output from this low-luminosity active galactic nuclei (AGN) is sufficient to power this outflowing wind, which in turn, has enough energy to counterbalance the cooling of both the warm and cool gas within Akira, and thereby suppress star formation.

While Akira is an ideal case-study, perhaps the most exciting aspect of this study is the fact that there are many more red geysers. Red geysers make up about 10% of quiescent galaxies at moderate stellar masses (2×1010 solar masses), which could have important implications on the duty cycle of this kind of supermassive black hole feedback. Moreover, because they are relatively common, red geysers may exemplify how typical quiescent galaxies maintain their quiescence.

An artist view of the universe 艺术家眼里的宇宙

Recently, a Chinese artist, Jian Yang, organized his personal exhibition in Beijing, China. The exhibition is called “the beginning of infinity” and one of his art pieces showed in this exhibition has a component made of an SDSS plate.

最近中国的一位艺术家杨健在北京进行了一次个人艺术展。这次展出的名字叫 “无穷的开始”,而其中的一件艺术品是利用了SDSS的一块光纤插板做成的。

The room holding the exhibition was designed as a maze. The art piece with the SDSS plate was placed at the center of a maze. It is named “The Universe” and the idea came from an old fairy tale: The earth is a big whale and the sky is a huge elephant. If you could find a leg of the elephant and climb up along the leg, then you could grab the stars. In the artist’s view, the SDSS telescope is trying to capture and analyze the starlight. So he combined science and the fairy tale by putting the SDSS plate at the bottom of the flying elephant’s leg, which means the plate could help us climb up and reach the stars.

展览的场地被别出心裁的设计成了迷宫的模式。而这件包含SDSS光纤插板的艺术品就被放置在迷宫的正中央。作品的灵感来源于艺术家小时候听到的神话故事:说大地是一只鲸鱼,宇宙是一只巨大的大象,如果你能找到大象的腿,往上爬就能抓到星星。对于艺术家来说,SDSS项目就是在做捕获分析星光的工作。杨健把SDSS光纤插板当作一只升腾起来的大象的脚底板,通过这种形象的建构来联合中国与国际,神话和科学。

 

The room holding the exhibition was designed as a maze.

The room holding the exhibition was designed as a maze. 整个展览场地被设计成一个迷宫的形式。

 

The art piece with an SDSS plate (plate# 3939).

The art piece with an SDSS plate (plate# 3939). The plate (编号3939) is placed at the bottom of an elephant’s leg. 用SDSS光纤插板做成的艺术品. SDSS的板子被当做大象的脚底板。

 

The art piece viewed from the bottom.

The art piece viewed from the bottom. 从下面看这件艺术品。

Tweep of the Week: Patrick Gaulme

Still Life of Patrick Gaulme with Telescope. Credit: Arl Cope

Still Life of Patrick Gaulme with Telescope. Credit: Arl Cope

Our @sdssurveys Tweep of the Week for the week of March 27th is Patrick Gaulme, stellar and planetary astronomer and part of the observing team for SDSS. Patrick will be at Apache Point Observatory for part of this week, taking observations for @MaNGASurvey, @APOGEEsurvey, and @eBOSSurvey. Fingers crossed for clear skies, low humidity, and calm winds. Now we also turn the blog over to Patrick to introduce himself:

 

Hello, my name is Patrick Gaulme, I have been an SDSS astronomer for about two years. I am also a researcher in the field of seismology of stars and giant planets. I am science PI of a NASA-ADAP grant to study eclipsing binaries detected by the NASA Kepler space telescope, and PI of several observation projects with K2, the resuscitated version of Kepler.

I am involved in developing techniques and methods to measure planetary atmospheric dynamics with Doppler imaging in the visible domain. For this I am science PI of the NASA-EPSCoR granted JIVE in NM instrument project, which is a Doppler imager aiming at detecting oscillations of Jupiter and Saturn and measure winds of thick atmospheres in our solar system.

Tweep of the Week: Audrey Oravetz

This week our @sdssurveys Twitter account will be run by SDSS observer, Audrey Oravetz. Audrey is part of the staff of observers and fiber optic technicians (the people who plug optical fibers into the plates) working for SDSS at our survey telescope in Apache Point, New Mexico (our telescope is neither automated, nor robotic, despite the common misconception!).

Audrey Oravetz

SDSS Observer, Audrey Oravetz (she’s definitely not a robot).

Here’s Audrey introducing herself in her own words:

Hello. My name is Audrey Oravetz and I have worked as an observer for the 2.5m SDSS telescope for the past nine years. It was always a dream of mine to work at a high-ranking observatory. I enjoy working alongside my colleagues to output a high quantity of quality data for the SDSS projects.

I graduated from the University of Colorado at Boulder in 2007 with a B.A. in Astrophysics and graduated from NMSU with a M.S. degree last summer. My thesis (under the supervision of Dr. Rene Walterbos (NMSU)) was centered around the study of ionizing H-alpha photons within two star formation nebulae, NGC346 and NGC602, within the SMC.

A Docufeest in New York.

This week many of the Key People in SDSS-IV have been meeting in New York to get a good start on the Documentation that is needed to accompany the upcoming Thirteenth Data Release (DR13) of the surveys (scheduled for July 2016).

Docufeest (scientists working on laptops)

SDSS-IV scientists hard at work at Docufeest.

Here a storify from Twitter of all the documentation fun we have been having at Docufeest. You will have to wait to see the updated website until the summer.

A Winter Night at APO

It’s almost March, and spring is in the air in much of the Northern Hemisphere, but here’s a beautiful Haiku written by SDSS Observer Patrick Gaulme as part of his SDSS 2.5m Observing Log for the night of Monday January 4th 2016 [Observed 1.5 h – Lost 9.9 for weather].

– A Winter night at APO –

No water in the faucets
Few photons in the bucket
Silent snow in the dead of night

AWinterNightatAPO

A winter night at APO, Image Credit: Patrick Gaulme, SDSS.

We all agree this lovely poem really captures the essence of observing in a snowy night, and we also think it demonstrates the huge range of talent found amongst the dedicated crew of SDSS observers working at Apache Point Observatory.

A Fundamental Constant of Nature through the SDSS — Una constante fundamental de la Naturaleza a través del SDSS

(The following is a guest post by Franco Albareti, a PhD candidate at Universidad Autónoma de Madrid. It is based on recent work with co-workers Johan Comparat and Francisco Prada, which was published last year in the Monthly Notices of the Royal Astronomical Society.)

The physical models we use to describe the world around us and predict new phenomena have some free parameters or constants. These parameters must be adjusted to what is experimentally observed. Among them, those known as the fundamental constants of Nature play a central role in our theoretical understanding of physics.

Los modelos físicos que usamos para describir el mundo a nuestro alrededor y predecir nuevos fenómenos contienen parámetros o constantes sin determinar. Estos parámetros deben ajustarse según lo que se observa experimentalmente. Entre ellos, aquellos conocidos como las constantes fundamentales de la Naturaleza desempeñan un papel fundamental en nuestra comprensión teórica de la Física.

In particular, the fine-structure constant (informally called “α”) tells us the strength of electromagnetic interactions. These interactions are responsible for most of the natural phenomena around us. The correct understanding and description of how they work is not only one of the major achievement of science, but had a tremendous impact on modern life, for instance in telecommunications. The BOSS cosmological survey, one of the surveys within SDSS, has constrained the time variation of the fine-structure constant or, alternatively, the strength of the electromagnetic interactions over more than half the age of our Universe (7 Gyrs).

En particular, la constante de estructura fina (para los amigos, “α”) nos da información sobre la fuerza de las interacciones electromagnéticas. Estas interacciones son responsables de la mayoría de los fenómenos naturales que nos rodean. El hecho de que seamos capaces de entender y describir correctamente cómo funcionan, no sólo es uno de los grandes hitos de la Ciencia, sino que también ha tenido un impacto radical en nuestra forma de vida, por ejemplo, en las telecomunicaciones. El cartografiado cosmológico BOSS, uno de los cartografiados que forman parte del SDSS, ha restringido la variación temporal de la constante de estructura fina o, en otras palabras, la fuerza de las interacciones electromagnéticas durante un período de tiempo que abarca más de la mitad de la edad del Universo (7 Ga).

Any change in the fine-structure constant value will leave its imprint on the separation between two characteristic spectral lines of oxygen, see figure 1 below. These lines are emitted by quasars (extremely luminous galaxies whose light reaches us from the furthest places in the Universe). Thus, a bigger or smaller separation between those lines means that the electromagnetic interactions were stronger or weaker when the light was emitted.

Cualquier cambio en el valor de la constante de estructura fina afectará la separación entre dos líneas espectrales del Oxígeno (ver figura 1). Estas líneas son emitidas por cuásares (galaxias extremadamente luminosas cuya luz nos llega desde los lugares más recónditos de nuestro Universo). Una separación mayor o menor entre estas líneas espectrales significa que las interacciones electromagnéticas eran más fuertes/débiles cuando la luz fue emitida.

Doubly-ionized oxygen lines [OIII] observed in a BOSS quasar spectrum. Líneas espectrales de Oxígeno doblemente ionizado [OIII] observadas en un espectro de un cuásar tomado por BOSS.

Figure 1. Doubly-ionized oxygen lines [OIII] observed in a BOSS quasar spectrum.
Líneas espectrales de Oxígeno doblemente ionizado [OIII] observadas en un espectro de un cuásar tomado por BOSS.

Members of the SDSS collaboration have concluded that the value of the fine-structure constant has remained the same over the last 7 billions years in 1 part in 50,000 (figure 2). For this, more than 10,000 quasar spectra collected by BOSS were used (figure 3).

Miembros de la Colaboración SDSS han concluido que el valor de la constante de estructura fina no ha variado durante los últimos 7 mil millones de años en más de una parte en 50.000 (figura 2). Para ello. más de 10.000 espectros de cuásares tomados por BOSS han sido analizados (figura 3).

Measurements of the variation of the fine-structure constant (Δα/α) as a function of redshift (left panel) and line intensity (right panel). The grey bands in the left figure indicate regions where the sky contamination is strong and, therefore, it affects the measured value. Medidas de la variación de la constante de estructura fina (Δα/α) en función del corrimiento al rojo (imagen izquierda) y la intensidad de las líneas (imagen derecha). Las bandas grises en la figura de la izquierda indican las regiones donde la emisión del cielo es fuerte y, por tanto, afecta al valor medido.

Figure 2. Measurements of the variation of the fine-structure constant (Δα/α) as a function of redshift (left panel) and line intensity (right panel). The grey bands in the left figure indicate regions where the sky contamination is strong and, therefore, it affects the measured value.
Medidas de la variación de la constante de estructura fina (Δα/α) en función del corrimiento al rojo (imagen izquierda) y la intensidad de las líneas (imagen derecha). Las bandas grises en la figura de la izquierda indican las regiones donde la emisión del cielo es fuerte y, por tanto, afecta al valor medido.

Figure 3. Left panel: Composite image with all the BOSS quasar spectra used in this research (10,363) sorted by redshift (each horizontal line is a quasar spectrum). The displacement of the spectral lines to larger wavelengths (effect known as redshift) is due to the cosmological expansion of the Universe. Right panel: Composite image centered on the Oxygen lines and horizontally displaced to account for the redshift effect. Imagen izquierda: Conjunto de todos los espectros tomados por BOSS que han sido usados en la investigación (10.363) ordenados según el corrimiento al rojo (cada línea horizontal es un espectro de un cuásar). El desplazamiento de las líneas espectrales hacia longitudes de onda más largas (efecto conocido como corrimiento al rojo) es debido a la expansión cosmológica del Universo. Imagen derecha: Misma imagen anterior centrada en las líneas de Oxígeno y corrigiendo el desplazamiento horizontal para tener en cuenta el corrimiento al rojo.

Figure 3. Left panel: Composite image with all the BOSS quasar spectra used in this research (10,363) sorted by redshift (each horizontal line is a quasar spectrum). The displacement of the spectral lines to larger wavelengths (effect known as redshift) is due to the cosmological expansion of the Universe. Right panel: Composite image centered on the Oxygen lines and horizontally displaced to account for the redshift effect.
Imagen izquierda: Conjunto de todos los espectros tomados por BOSS que han sido usados en la investigación (10.363) ordenados según el corrimiento al rojo (cada línea horizontal es un espectro de un cuásar). El desplazamiento de las líneas espectrales hacia longitudes de onda más largas (efecto conocido como corrimiento al rojo) es debido a la expansión cosmológica del Universo. Imagen derecha: Misma imagen anterior centrada en las líneas de Oxígeno y corrigiendo el desplazamiento horizontal para tener en cuenta el corrimiento al rojo.

Animation -> The animation below shows an image of a quasar, its full optical spectrum (bottom left), a zoom in the oxygen lines used for the analysis (bottom right), and the measured value of the variation of the fine-structure constant as a function of redshift (top panel). It only displays 200 objects among the >10,000 quasars used for the research. (It starts slow so you can pay attention to all of the information, but then it goes faster)

Animación -> Esta animación muestra una imagen de un cuásar, junto con su espectro en el óptico (parte inferior izquierda), un zoom en las líneas de Oxígeno usadas para el análisis (parte inferior derecha), y el valor medido de la variación de la constante de estructura fina como función del corrimiento al rojo (parte superior). La animación sólo muestra 200 objetos de entre los >10.000 cuásares usados para la investigación. (Empieza despacio para que uno se pueda fijar en toda la información que se muestra, pero luego empieza a ir más rápido.)

alpha_spectra_small

Animation of the measured change in the fine structure constant with cosmic time. You may need to refresh this page to see the animation again.

To reach further in the past, when the Universe was five times younger, a dedicated observational program, APOGEE-Q (APOGEE Quasar Survey), is being developed in order to not only measure a variation on the fine-structure constant, but study supermassive black hole masses and quasar redshifts. This program will use an infrared spectrograph from the APOGEE survey instead of the optical one used by BOSS. This allows us to observe the infrared region of the electromagnetic spectrum, where the oxygen lines emitted by distant quasars are found due to the cosmological expansion of the Universe. It will start to take the first data during 2016.

Para remontarnos todavía más atrás en el tiempo, cuando el Universo era cinco veces más joven, un programa observacional específico, APOGEE-Q: APOGEE Quasar Survey, está siendo desarrollado para, no sólo medir la variación de la constante de estructura fina, sino también para estudiar agujeros negros súper masivos y corrimientos al rojo de cuásares. Este programa usará un espectrógrafo infrarrojo del cartografiado APOGEE en vez del espectrógrafo óptico usado por BOSS. Esto nos permitirá observar la región infrarroja del espectro electromagnético, que es donde se encuentran las líneas del Oxígeno emitidas por cuásares muy lejanos debido a la expansión cosmológica del Universo. El programa empezará a tomar los primeros datos en 2016.

Astronomers studying galaxy mergers using MaNGA data

(The following is a guest post by Lihwai Lin, an assistant research fellow at Academia Sinica, Institute of Astronomy and Astrophysics. She is curretnly chairing the MaNGA merger working group and organized the MaNGA merger mini-workshop described in the article below.)
Galaxies are not isolated. During the lifetime of galaxies, they may encounter another galaxy and merge together to become a larger one. Mergers can induce gas to flow toward the inner parts of galaxies through tidal forces, triggering starbursts or even “switching on” a galaxy’s central black hole (the result is called an “active galactic nucleus,” or AGN). As a result of rapid gas consumption during mergers, a galaxy may lose the majority of its gas and end up as a “dead” system with little on-going star formation. This kind of merger event is rare, but is suggested to be an important process that transforms star-forming galaxies into the quiescent population. One of the key sciences that MaNGA is attempting to address concerns the role of galaxy interactions and mergers in shaping the properties of galaxies. With just one year of the MaNGA survey, we have obtained Integral Field Unit (IFU) observations for ~150 paired galaxies, ranging from early encounters to post-mergers.
Examples of galaxy pairs selected from the SDSS. The magenta hexagons represent the IFU coverage of MaNGA. (Credit: SDSS)

Examples of galaxy pairs selected from the SDSS. The magenta hexagons represent the IFU coverage of MaNGA. (Credit: SDSS)

In early November of 2015, experts studying galaxy mergers gathered together in Taipei for the “SDSS-IV/MaNGA mini-workshop on galaxy mergers”. This 3-day workshop consists of 6 invited talks, 5 contributed talks, plus 2 discussion sessions devoted to theoretical and observational efforts, chaired by Jennifer Lotz (STScI) and Sara Ellison (University of Victoria) respectively.

Participants for the MaNGA mini-workshop on galaxy mergers, held at Academia Sinica, Institute of Astronomy and Astrophysics (ASIAA), Taipei, on Nov. 4-6, 2015.

Participants for the MaNGA mini-workshop on galaxy mergers, held at Academia Sinica, Institute of Astronomy and Astrophysics (ASIAA), Taipei, on Nov. 4-6, 2015.

With MaNGA’s spatially resolved observations for merging galaxies, we can study not only where and when the star formation is triggered and shut down during the process of  galaxy interactions, but also how the massive black holes in the center of galaxies can be fueled and grow through galaxy mergers. The observational results from MaNGA will also be compared in great detail with theoretical predictions from state-of-art simulations. Stay tuned for more exciting science that will come from MaNGA!

How SDSS Talked about Light for #IYL2015

This is a re-posting of the wrap-up article which appeared on the IYL2015 main blog.


 

2015 has been the International Year of Light.

As astronomers, here at the Sloan Digital Sky Survey everything we do is based on collecting light from cosmic objects. So we have been pleased to celebrate the International Year of Light, and especially the Cosmic Light Theme, supported by the IAU.cosmiclight_color_whitebgAs a small contribution to this celebration, every month in 2015 SDSS had a special blog post talking about the different ways we use light. Here’s a roundup of what we talked about through out the year.

In January we talked about How SDSS Uses Light to Study the Darkest Objects in the Universe. This blog post, by Coleman Krawcyzk and Karen Masters (both from the University of Portsmouth in the UK) with help from Nic Ross (Royal Observatory, Edinburgh) was about finding black holes by looking at the light from distant galaxies. Finding objects which are famous for not emitting any light, using light seems contradictory, but this article explains how the light created by the hot material falling onto a black hole can make these objects outshine the entire galaxy they live in.

Quasar

An artist’s rendition of a quasar created by Coleman Krawczyk (ICG Portsmouth). The image is drawn on a radial log scale with the central black hole 1 AU in size.

In February we wrote about How SDSS Uses Light to Measure the Distances to Galaxies. This of course was about the technique of measuring galaxy redshifts (ie. the shift of their light to longer wavelengths caused by the expansion of the Universe) by looking at absorption and emission lines in galaxy spectra and comparing their wavelength to the laboratory measurement. Edwin Hubble, and others, realised over 80 years ago, that this can be used to give distances to galaxies, as the amount of redshift increases with the galaxy’s distance. The original motivation for SDSS (back in the 1990s) was to used this technique to measure distances to a million galaxies, and in SDSS-IV we are continuing to use this in the eBOSS part of the survey, to map distances to ever more distant galaxies.

A map of the Universe from SDSS where the distance to galaxies is given in terms of their redshift. Credit: SDSS

A map of the Universe from SDSS where the distance to galaxies is given in terms of their redshift. Credit: SDSS

In March, we came back to the most local Universe, with a post by SDSS-IV Spokesperson, Jennifer Johnson (Ohio State University) on How SDSS Uses Light to Understand Stars Inside and Out in the Kepler Field. This was about part of the APOGEE survey, which is measuring spectra from stars which have light curves measured by the Kepler Satellite. This is a valuable experiment, as the combination of spectra and light curves allows us to measure the masses, ages and compositions of these stars.

The Kepler Field. Credit: NASA

The Kepler Field. Credit: NASA

In April, we moved back outside our own Galaxy, to measuring the invisible mass in other galaxies, with a post on How SDSS Uses Light to Explore the Invisible, by the MaNGA Lead Observer, and SDSS-IV Data Release Co-ordinator, Anne-Marie Weijmans from St Andrew University. This post talked about how MaNGA is measuring spectra across the face of nearby galaxies in order to get measurements of the internal motions (again using the redshift/blueshift of the spectra). These measurements give a way to measure the total mass of galaxies, which we find in all cases is much much more than the mass in stars.

MaNGAlogo5small

For May we went back in the history of SDSS, and talked about How SDSS Used Light to Make the Largest Ever Digital Image of the Night Sky. This post was about the the SDSS camera and the SDSS imaging survey, which ran from 2000-2008, and created a image of over 30% of the sky, containing over a trillion pixels (an image which dwarfs others that have also been claimed as the largest).

The SDSS Camera, now in storage in the Smithsonian Museum. Credit: SDSS, Xavier Poultney

The SDSS Camera, now in storage in the Smithsonian Museum. Credit: SDSS, Xavier Poultney

June also saw a post about SDSS imaging, and about an unexpected use for them, finding asteroids, in How SDSS Uses Light to Find Rocks in Space. This has been beautiful visualized in the below video, by Alex Parker.

If our posts in February, March and April confused you because you didn’t understand what astronomers mean by measuring spectra, then the July post was for you: “How SDSS Splits Light into a Rainbow for Science”.  This post explained all about what spectra are, how to create them with gratings, and contained a with bonus activity to make your own spectroscope created by the SDSS Education and Public Outreach group.

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).Credit: Wikimedia

Our August post, by the APOGEE survey Public Engagement officer, David Whelan (from Austin College, Texas)  was about the basic physics of the most abundant element in the Universe (hydrogen): “How SDSS Uses Light to Study the Most Abundant Element in the Universe.”

For September, we visited an IYL2015 Exhibit in Dresden with Zach Pace, Graduate Student at the University of Wisconsin, Madison. Zach reported on SDSS plates on display in the exhibit, linking back to an earlier post in which we explain why we need all these big aluminium plates to do our spectroscopic survey. IYL2015 – SDSS Plates (in Retirement).

Technische_Sammlungen3

SDSS Plate on Exhibit in Dresden.

We went back to the APOGEE survey in October, with a post by Gail Zasowski (from John’s Hopkins University) on How SDSS uses mysterious “missing” light to map the interstellar medium. In this post we learned about how SDSS has helped shed light on the the mystery of missing light caused by absorption in the material which is found between stars in our own Galaxy.

Finally last month, we talked about How SDSS Uses Light to Measure the Mass of Stars in Galaxies. Looking back to the post in February, we claimed that the total mass of galaxies is always much much more than the mass we can count in their stars. But how do we know how much mass is in the stars in a galaxy? This post explains how that can be done using measurements of the light from galaxies.

So that wraps up a year of the celebration of light in the SDSS. We certainly haven’t covered all the ways in which SDSS astronomers are using light to learn about the Universe around us, from asteroids in the solar system, to stars in our own Galaxy and galaxies are the furthest edges of the Universe. But we hope it gives you a flavour for the kinds of things the light collected by SDSS (both images and spectra) can be used for.

If you’re looking for a guided entry into SDSS science (especially suitable for educational use), please visit our Voyages.sdss.org site to discover guided journeys through the Universe. As always all SDSS data (through our 12th public data release, DR12) is available free to download, and look out for DR13 (including the first data from SDSS-IV) coming up in mid 2016.

 

Building the APOGEE-2S Spectrograph: Putting Together All the Little Pieces

Building a spectrograph is no mean feat — and an instrument like the APOGEE spectrograph, with high expectations of precision to meet its mighty science goals, takes time and effort. Today we want to share with you some of the many highlights of the ongoing, and exciting, work being done to make the APOGEE-2S spectrograph, the “twin” spectrograph that is going to perform survey operations on the du Pont Telescope at Las Campanas Observatory in Chile.

Spectrographs have several key components. The light collected by the telescope from a star is collimated by a great big lens before it strikes the diffraction grating, which splits the light into its constituent colors (it’s a fancy prism). The “split” light then travels through a camera so that it can be refocused onto the infrared array, which records the spectrum of the star.

With that in mind, here’s a picture of a part of the collimator known as the collimator positioning actuator, which is the little piece of metal seen at the center of the test dewar (the large cylinder). Its role is to precisely position the collimator lens, to ensure precise collimation at all times.

Josh Peebles from Johns Hopkins is seen here preparing the collimator positioning actuator for cryogenic testing.

Josh Peebles from Johns Hopkins is seen here preparing the collimator positioning actuator inside of a dewar for cryogenic testing.

Next we have some fancy-looking lenses. Because APOGEE works with infrared wavelengths, the lenses have to be made out of substances that are transparent to infrared light, not visible light. As a result, they are actually opaque at visible wavelengths. In the picture below, the lens appears green to us, but this fused silicon lens would be see-through if we had infrared-sensitive eyes.

This is one of the APOGEE-2S spectrograph's lenses (there are six of them in total) up close. It is made of fused silicon, is opaque to our eyes, but is transparent to infrared light. You can see light reflecting from its surface in this photo

This is one of the APOGEE-2S spectrograph’s lenses (there are six of them in total) up close. It is made of fused silicon, and is transparent to infrared light.

New England Optical Systems installed these lenses into the camera barrels — the black cylinders shown below — which will be attached to form the spectrograph’s camera (see further below).

In November, New England Optical Systems finished installing the lenses into the camera barrel.

In November, New England Optical Systems finished installing the lenses into the camera barrel.

As of just a few days ago, the camera is now fully assembled, and is currently undergoing tests to ensure that it is working to specifications.

The spectrograph camera is fully assembled, and undergoing a test called laser unequal path interferometry (LUPI for short).

The spectrograph camera is fully assembled, and undergoing a test called laser unequal path interferometry (LUPI for short).

This little photojournal makes building a multi-million dollar spectrograph look so neat and tidy! One final picture to disillusion you. Below is Matt Hall, one of the technicians at the University of Virginia assisting with the build. In this picture, he is testing springs that are used to hold some of the lenses in place. It sounds strange that springs are part of a lens system; but because the APOGEE-2S spectrograph is going to be cooled cryogenically, the lenses will all shrink a little. These springs apply pressure to the edges of the lenses so that they stay in place when they shrink.

This picture illustrates the secret to building instruments like the APOGEE-2S spectrograph: every big piece, like the collimator or camera, is made up of dozens or even hundreds of small, interconnected and interdependent pieces. And each little piece has to be built and tested to ensure that it does its job properly. So here’s to the people, both in Chile and in the U.S., who are currently dedicating their time and effort to build the best spectrograph possible. We look forward to making good use of it!

Matt Hall (UVa) is seen here testing the spring constants of individual spring plungers. As with every small part of the build, it is dealt with meticulously and thoroughly so that the completed spectrograph works at this highest level possible.

Matt Hall (UVa) is seen here testing the spring constants of individual spring plungers. As with every small part of the build, it is dealt with meticulously and thoroughly so that the completed spectrograph works at the highest level possible.