We are here live at the American Astronomical Society meeting in National Harbor, Maryland, where this afternoon the SDSS announced some exciting new results. We have used Baryon Acoustic Oscillations (BAOs) to measure the most precise distances to galaxies all the way across the universe. This illustration shows how this technique works: we know from the early history of the Universe that galaxies are more likely to be separated by 450 million light-years than 350 or 550 million. We can use that knowledge to make highly accurate distance measurements, which tell us about the nature of the Universe we live in.

Image credit: Zosia Rostomian, Lawrence Berkeley National Laboratory

Read more about it in our press release!

News coverage about this story is already starting to appear. Check back on this page for links to stories!

Over 80 astronomers attended the 2013 BOSS Collaboration Meeting held at the Lawrence Berkeley National Laboratory, from December 9th to 11th. During the meeting we had active and involved discussions about at all the great results that are coming out from the over 2 million spectra already taken with the BOSS spectrograph.

(Image Credit: Berkeley Lab – Roy Kaltschmidt)

Final discussions on the Data Release 11 papers, as well as preparation for the upcoming final BOSS Data Release 12, were two of the main topics in the meeting, but there were also many new exciting results from the different working groups covering topics such as quasars, galaxies, and clouds of gas in distant galaxies.

The conference dinner, at the Chabot observatory, was preceded by a great talk on exoplanets by Sarah Ballard, and followed by observations of Jupiter’s satellites using telescopes almost a hundred years old. On Wednesday afternoon, the first BOSS soccer championship ended up with a tight score (Quasars 3 – Lyman alpha 5), surprisingly no injuries and a lot of fun!

A massive thank you to Qingqing Mao a PhD student from Vanderbilt who is running SDSS Social Media sites in Chinese (Simplified Mandarin). We have both Facebook and Weibo (Chinese version of Twitter) accounts for SDSS. Below is a wordl of the most common characters used by these accounts. The blue characters in the middle are a phonetic translation of “Sloan”. “Tian Wen” also appears many times – literally “sky language/culture” – meaning astronomy (e.g. “tian wen xue” means the study of astronomy).

A recent Nature editorial argues for the need to support lab-based basic spectroscopy to fully understand the wealth of astronomical data coming from surveys such as SDSS-III and its APOGEE spectrograph.  In particular such spectra contain many atomic and molecular transitions only very rarely studied in Earth-based laboratories.  Understanding the relative strengths of these transitions will be important in using them to fully measure the abundance of elements and molecules in stars in our Milky Way galaxy.

http://www.nature.com/news/nailing-fingerprints-in-the-stars-1.14239

Today’s blog is a guest post by SDSS astronomer Guangtun Zhu of Johns Hopkins University

For more than a decade, SDSS astronomers have been mapping all the galaxies of the Universe – but what about the space between the galaxies? How can we map whatever cold, dark gas might be there?

When we look at spectra of distant quasars, we learn not only about the quasars, but also about whatever the light passed through on its journey from quasar to telescope. In this case, absorption lines in the quasar spectra reveal gas in intergalactic space. The SDSS has obtained spectra for more than 200,000 quasars, providing a map of gas absorption across the sky.

Mapping the distribution of matter between galaxies is one of the greatest challenges in modern astronomy. When we look up in the sky, even with the largest telescopes, we see mostly dark space between galaxies that appears to be totally empty. Theories of cosmology predict that most of the matter in the Universe should be in the form of diffuse gas between galaxies, but actually detecting that gas is extremely challenging because it emits essentially no light.

A team of SDSS-III scientists led by me and my Johns Hopkins colleague Brice Ménard has just finished a study that takes on this difficult task. Using new advanced statistical techniques, we have been able to detect the very weak but clear signature of magnesium in intergalactic space. Those techniques allowed us to find how the amount of gas around galaxies changes with increasing distance from the center of the galaxies. Our findings are summarized in a paper submitted to the journal Monthly Notices of the Royal Astronomical Society, and available on the arXiv preprint server:

“The Large-scale Distribution of Cool Gas around Luminous Red Galaxies”
http://arxiv.org/abs/1309.7660

To detect gas in the intergalactic space, we used its absorption effects. When light from a distant source passes through a gas cloud, photons at a specific energy are absorbed, leaving a valley in the source’s spectrum.

The light sources we used are quasars – very bright objects powered by supermassive black holes at the centers of distant galaxies. Quasars are the brightest things in the Universe, so they do an excellent job of shining through the intergalactic gas we want to study. And the SDSS has obtained spectra of more than 200,000 quasars, letting us see the signal of intergalactic gas all over the sky.

Most of the gas absorption, however, is so weak that its signature is hidden by variations in the quasar spectra themselves. So even with the huge dataset we have, we had to use new statistical techniques to find the gas. Using a sample of one million galaxies that lie between us and thousands of distant quasars, we looked at the place in the quasar spectrum corresponding to magnesium. Our statistics showed us that, on average, the quasars appeared to be missing 0.01% of the magnesium. In other words, out of every 10,000 photons emitted by a quasar at the right wavelength, 9,999 made it to Earth, and one didn’t show up because it was absorbed by magnesium between galaxies. This effect is way too small to see for any individual quasar – we can only find it by averaging the light from all the quasars, all over the Universe.

So now that we know that the intergalactic gas is there, what’s next? The “standard model” of cosmology makes certain predictions about how matter is distributed in the Universe. So far, the model’s predictions have matched up extremely well with observations of the distribution of galaxies. Will the model also correctly predict the distribution of intergalactic gas? Our research shows, for the first time, that the large-scale distribution of gas in the Universe is consistent with the standard model.

This graph shows how the amount of gas around an average galaxy changes with increasing distance. The blue points show our latest results. The green and orange lines show the predicted amount of gas associated with that galaxy (green) and the galaxies around it (orange). The blue curve is the sum of the orange and green curves. The graph shows that the observed amount of gas matches predictions very well.

New surveys such as SDSS-IV, the next phase of the SDSS, are now being prepared and will soon provide us with even more data to help us map the distribution of matter in space with even higher sensitivity. Astronomers will be able to map different elements around different types of galaxies, across cosmic time. These observations will lift the veil of the universe and reveal the overall distribution of matter. In addition, they will provide new clues to a better understanding of the formation and evolution of galaxies like our own Milky Way.

The future is bright for studies of dark regions in space.

SDSS-III Data Release 10 features crowd-sourced classifications of the shape of 304,122 galaxies from images taken by SDSS. The paper describing these data is in press at the Monthly Notices of the Royal Astronomical Society and is available on the arXiv preprint server: “Galaxy Zoo 2: detailed morphological classifications for 304,122 galaxies from the Sloan Digital Sky Survey”.

This paper was led by Galaxy Zoo science team member Kyle Willet, from the University of Minnesota, and presents morphological classifications for 304,122 SDSS galaxies constructed from over 60 million clicks contributed by members of the public at the Galaxy Zoo website.

You can read more about the paper on the Galaxy Zoo blog (http://blog.galaxyzoo.org/2013/08/19/galaxy-zoo-2-data-release/)

The data described in this paper are available through both Galaxy Zoo at http://data.galaxyzoo.org, and through SDSS-III Data Release 10 at http://www.sdss3.org/d110

Galaxy Zoo work continues at http://galaxyzoo.org. On the site right now members of the public are looking at more images from the SDSS (the full DR8 imaging area) as well as some from the Hubble Space Telescope. The Galaxy Zoo team is also working hard to bring you images of your favourite galaxies in the infrared soon.

The Sloan Digital Sky Survey III (SDSS-III) has just released the largest comprehensive sample of high-resolution infrared spectra of 57,000 stars in our Milky Way.

Data Release 10 is the latest in a series of data releases stretching back to 2001. This release includes the first data from the Apache Point Observatory Galactic Evolution Experiment (APOGEE), and includes an additional year of data from the ongoing SDSS-III Baryon Oscillation Spectroscopic Survey (BOSS). APOGEE is obtaining R~22,500 spectra of 100,000 red giant stars sampled through the bulge, disk, and halo of our galaxy. These spectra allow astronomers to determine radial velocities, temperatures, surface gravities, and abundances of elements in these stars.

BOSS has now obtained spectra for almost 1.4 million objects, including 860,000 galaxies and 105,000 quasars from (2<z<3.5), as part of its quest to measure the positions of 1.5 million massive galaxies over the past six billion years of cosmic time, as well as 160,000 quasars — giant black holes actively feeding on stars and gas — from as long ago as 12 billion years in the past.

DR10 is available at: http://www.sdss3.org/dr10.

READ THE PRESS RELEASE HERE

SDSS-III scientists in the Baryon Oscillation Spectroscopy Survey (BOSS) have just completed the second phase of a project to provide a map of the observable universe showing the positions of giant clouds of hydrogen gas. BOSS is mapping the Universe by measuring the positions of galaxies, clusters of galaxies, and clouds of hydrogen gas. These maps allow astronomers to understand the history of the universe, starting with the Big Bang all the way through to the formation of the galaxies, stars, and planets that provide the site for the development of life.

Hydrogen is the most abundant element in the Universe. Thus measuring the position of hydrogen gas clouds reveals important details on the distribution of normal matter in the Universe. To detect these hydrogen clouds, BOSS uses super-luminous quasars as backlights. Quasars can be billions of times brighter than the Sun and are currently thought to be powered by matter falling into super-massive black holes. The quasars that BOSS uses as backlights are located billions of light-years from us, when the Universe was one fifth its current age of 13.7 billion years.

Because light travels at a finite speed (186,000 miles per second) this extreme distance means that we are also looking further back in time, back to when things in the Universe were closer together. As the light travels from the quasar to us, the Universe has expanded and so the light from the quasar is stretched out – a phenomenon known as redshift.

The light that the BOSS detector receives is partially absorbed by the intervening gas clouds and the pattern of absorption gives a map of the gas. Each gas cloud absorbs at a wavelength particular to a given energy transition in hydrogen.
The redshifting of the quasar light means that each cloud leaves an imprint at a different wavelength in the light we eventually observe from the quasar. The amount of absorption in the quasar spectrum at any given wavelength reveals the position of a hydrogen gas cloud between us and the quasar.

A map of the entire Earth at first glances reveals large features like continents, but reveals mountains, hills, and valleys when you zoom in. In the first phase of BOSS, scientists used a very coarse-grained map of the absorption due to hydrogen to study the “large-scale structure” of the universe at scales of hundreds of million light years, analogous to studying the size and disposition of the continents on the surface of the Earth. BOSS’s “continents” were clouds typically many millions of light-years in size. BOSS found that the gas was arranged in a pattern that reflected sound waves that existed during the first 380,000 years after the big bang. The pattern gave information on the conditions in the universe at this time and confirmed that the Universe consists of a strange cocktail of normal matter, photons, neutrinos, dark matter (matter that doesn’t interact with light and that forms the bulk of galaxies), and the completely mysterious dark energy which is currently driving the increasing expansion rate of the Universe.

SDSS-III scientists are producing detailed numerical simulations of the universe to compare to BOSS observations. This image shows a simulated map of the gas clouds (the red blobs are clusters of galaxies and the blue filaments are lower-density gas regions), in a cube of the universe 65 million light-years on a side.

In the second phase of their effort, BOSS scientists have been able to zoom in using more sensitive techniques to study the “small-scale” structures, down to scales of a few million light years, analogous to the mapping the mountains on a continent. This increased resolution reveals the characteristics of the gas clouds that are on the brink of forming galaxies.

The new BOSS observations so far appear consistent with current theories of the composition of the Universe. But this new data is sufficiently precise that BOSS hopes to use it to glean information on one of the least understood ingredients of the cocktail: neutrinos. These (ghostly) objects move through the universe nearly at the speed of light and cannot condense to form galaxies. However, their presence has an effect on the map of the gas clouds. The speeding neutrinos dilute the pattern that seeded the gas clouds. Current measurements indicate that neutrinos have a tiny mass (about one billionth of the mass of an electron). The cosmological maps from BOSS reflect its effects on the “small-scale” structures of the universe. Further analysis will reveal new constraints on the mass density of neutrinos in the cosmos.

The paper “The one-dimensional Ly-α forest power spectrum from BOSS” by N. Palanque-Delabrouille et al. was recently submitted to Astronomy & Astrophysics and is available at http://arxiv.org/abs/1306.5896

[youtube=http://www.youtube.com/watch?v=ATAHrwwrNqk&w=500&h=375&rel=0&modestbranding=1]
A simulation of the interaction of dark matter, gas, stars, and neutrinos in forming the structure of galaxies we observe. The overall expansion of the Universe has been scaled out of this simulation to more clearly illustrate how the large scale structure forms. Previous work mapped hydrogen clouds on the scale of this box. The current work can map down to the scale of the red spheres shown here that are turning into galaxies.

This second image is a map showing the ghostly neutrinos, here drawn in yellow, in the same cube of universe. The only hint of condensation appears about the largest density region, in the center of the image. With further analysis BOSS scientists plan to explore this faint imprint on the structure of hydrogen clouds from neutrinos in the early Universe.

We in the Sloan Digital Sky Survey collaboration are deeply saddened by the news of the loss of 19 firefighters from the Granite Mountain Hotshots of Prescott, Arizona.

There is a closer connection between astronomy and these hotshot crews than many may know. Fire is the top threat to the observatories of the American Southwest. Our facilities are at dry and remote sites, typically high up in the pine forests that top the mountains. Summer fires are a perennial danger.

While the Apache Point Observatory where the SDSS facility is housed has been lucky to escape direct threat in the last twenty years, several other major observatories have had close calls. That catastrophe has been averted is due largely to the tremendous efforts of the wilderness firefighters and response teams that work to contain these fires and shape them away from inhabited areas. Their skill and strength in combating these fires is truly remarkable.

We don’t know whether any members of the Granite Mountain Hotshots worked on fires near our observatories, but their loss is dear to us nonetheless. We want to take this opportunity to thank all of the firefighters working in the forests of the Southwest for their dedication, and we want to recognize the important role that they play in American astronomy. Most importantly, we want to send our condolences to the families and friends of those lost in this tragedy.

Donations to help the families and coworkers of the firefighters who died battling the Yarnell Hill Fire can be made at the following website:

http://www.prescottffcharities.org/how-you-can-help/

Finally, we want to recognize the important work that goes on locally at our location. Fire prevention is a year-round activity at Apache Point Observatory (APO). APO Site Manager Mark Klaene is a Captain in the the High Rolls Volunteer Fire Department (VFD) and a Lieutenant in the Sunspot VFD. SDSS Engineer Tracy Naugle is a firefighter in the Sunspot VFD, and APO 3.5-m telescope observer Alysha Shugartis is a probationary firefighter in the Sunspot VFD. APO and SDSS specifically thank the Lincoln National Forest branch of the U.S. Forest Service for their efforts to manage the forest around APO and keep our observatory safe.

The White House recently recognized 13 individuals as “Champions of Change” for Open Science: people who worked to make data public for the greater good:
http://www.whitehouse.gov/champions/open-science

One of the thirteen was Princeton University’s Jeremiah P. Ostriker, recognized for his role in the development of the Sloan Digital Sky Survey. This recognition reflected SDSS’ record of making its data public to the world, enabling the writing of literally thousands of papers. The ceremony, which took place on June 20 in the Eisenhower Executive Office Building, adjacent to the White House, included an open discussion among the 13 Champions, as well as talks by John Holdren (Director of the White House Office of Science and Technology Policy) and Todd Park (Chief Technology Officer of the United States). Prof. Ostriker invited five guests to take part in the ceremony. The visiting group is shown here left-to-right starting from the upper left: Michael Strauss (former SDSS spokesperson), Al Sinisgalli (who was key in arranging Princeton’s financial support of the project), Don York (SDSS’ first director), Ostriker, Jill Knapp (scientist par excellence who kept the project going through sheer force of will) and Jim Gunn (SDSS Project Scientist).

(Image Credit: Anjelika Deogirikar)

SDSS astronomers at Ohio State have made a new, more robust measurement of the relationship between stellar mass and the abundance of elements heavier than helium and hydrogen. The measurement of elements is called the “gas-phase metallicity” and is based on measuring weak auroral lines that are typically undetected in galaxy spectra (dubbed the “direct method”). The relationship between these two is called the mass-metallicity relationship. To enhance the signal-to-noise ratio of these lines, the astronomers stacked ~200,000 galaxy spectra from the SDSS-II Data Release 7.

(Figure) The new mass-metallicity relation is shown by the points and black line. The colored lines indicate previous mass-metallicity relations based on less certain strong line methods. This new measurement of the mass-metallicity relation provides important constraints for galaxy evolution models, especially for the efficiency of galactic winds.

Lead author Brett Andrews has prepared a brief video describing the main results for a general audience:

For more details please see the published paper:
“The Mass-Metallicity Relation with the Direct Method on Stacked Spectra of SDSS Galaxies”
Andrews & Martini (2013)
The Astrophysical Journal, 765, 140.
http://arxiv.org/abs/1211.3418
http://adsabs.harvard.edu/abs/2013ApJ…765..140A

In April BOSS passed an impressive milestone with 2 million survey-quality spectra. These spectra now probe large volumes of the Universe. The galaxy spectra alone probe over 35 billion cubic lightyears (four cubic gigaparsecs), while the BOSS quasars probe an even larger volume but much more sparsely. BOSS is on pace to successfully complete its main survey of 10,000 square degrees, which is almost one quarter of the sky, by the end of SDSS-III observing in the summer of 2014.

Officially, the prize for the two millionth object goes to a spectrum of the blank sky.

Figure: The two-millionth BOSS spectrum: an observation of a blank region of the sky (green line). Most of the emission that is seen is from the Earth’s atmosphere. The peaks in the right half of the figure are emission lines from oxygen, water, carbon dioxide, and other molecules. After subtracting the sky, the remaining signal (black line) is consistent with no detected source. The quoted redshift in light green is the BOSS pipeline fitting a quasar so faint that it is entirely consistent with the noise from the observation; this is not a real detection of an object.

Why does BOSS intentionally take observations of blank regions in the sky?

It turns out that these sky spectra are actually vital to the basic analysis of the BOSS spectra of stars, galaxies, and quasars. Most of the photons detected by BOSS are emitted by the Earth’s atmosphere. We have to subtract these photons to analyze the faint signals of distant galaxies. About 10% of BOSS fibers on each plate are used to observe blank regions of the sky. BOSS takes these blank-sky observations to help in calibration and removing the sky background.

These blank sky spectra can also have scientific utility. These blank sky spectra are the easiest targets from which to study the diffuse interstellar medium, as done by Brandt & Draine:
http://arxiv.org/abs/1109.4175
They are also used to search for serendipitous observations of emission-line galaxies. While the fibers are placed in locations that the SDSS-III imaging data show to be blank, galaxies that emit most of their light in just a few emission lines can occassionally appear in these spectra. Such galaxies are very uncommon today and understanding their presence at high redshift (which is necessary for their ultraviolet emission lines to be observed in the visual region of the spectrum) can help us learn about the early process of galaxy formation.

Calcium (Ca) came from stars. Along with all other elements other than hydrogen, helium, and a bit of lithium, calcium was made in the fusion furnaces that power the immense amounts of energy given off by stars. To make calcium requires a star at least five times the mass of our Sun and is most efficiently produced by even more massive stars that explode as supernovae and distribute their elements to their surroundings[1]. What happens to this material and how it gets distributed around a galaxies is a key current question in the formation of galaxies.

SDSS-III members Guangtun Zhu and Brice Ménard (Johns Hopkins University) have just completed a study searching for Ca II around galaxies in SDSS Data Release 7. This paper has been submitted to the Astrophysical Journal and appears on today’s arXiv.org:

“Calcium H&K Induced by Galaxy Halos”
Guangtun Zhu, Brice Ménard
http://arxiv.org/abs/1304.0451

Using signatures imprinted in the spectra of distant quasars, they find that Ca II, calcium missing one of the two electrons in its outermost subshell, exists in the outskirts of galaxies, and there is a lot of it.

The search for Ca II used the Fraunhofer H&K absorption lines. These absorption lines were first discovered in the solar spectrum about 200 years ago. The wavelengths of these lines are defined by the amount of energy difference between the outermost electron of singly-ionized calcium to be in the 4s (l=0) instead of 4p state (l=1). The difference in energy between H and K is the difference between the spin of the electron (s=1/2) being in the same direction (more energy, labmda=396.8 nm, J=|l+s|=3/2) or in the opposite direction (less energy, lambda = 393.4 nm, J=|l-s|=1/2) as its orbital momentum around the nucleus[2].

When light passes through a cloud of Ca II, photons with wavelengths at 383.4 nm and 396.8 nm can be absorbed, leaving a signature in the light that passes through the cloud.

Examples of background quasars whose light passes near galaxies. Images and quasar spectra were both taken with the SDSS.

Thus the researchers set out to search for signs of a small amount of missing light at these wavelengths. However, the signature of Ca II absorption in an individual quasar spectrum is almost impossible to see. This study was thus only possible by combining the vast quantity of spectra made available by SDSS. By using the light from 100,000 background quasars that passes near galaxies in SDSS DR7, Zhu and Ménard found that significant amounts of Ca II were present up to 700,000 light years (200 kpc) away from the galaxies.

The image above shows the density of Ca II (right axis) as a function of the distance (rp) from the center of the galaxy. Significant amounts of Ca II are found all the way out to 200 kpc (700,000 light years).

The Ca II is more concentrated around star-forming galaxies than passive galaxies and is preferentially found above the plane of disk galaxies. These results are consistent with the Ca II coming from bipolar outflows from the galaxies that are driven by star formation. These outflows carry along many of the elements formed in the stars and released by supernovae.

This study is only sensitive to Ca in this ionization state where it has lost one electron. The distribution of neutral Ca or other ionization states remains unknown.

[1] http://en.wikipedia.org/wiki/Supernova_nucleosynthesis
[2] http://physics.nist.gov/PhysRefData/Handbook/Tables/calciumtable4.htm