Sky Surveys and the Virtual Observatory

Alex Szalay

The Johns Hopkins University

Living in an Exponential World

• Astronomers have a few hundred TB now– 1 pixel (byte) / sq arc second ~ 4TB

– Multi-spectral, temporal, … → 1PB

• They mine it looking for new (kinds of) objects or more of interesting ones (quasars), density variations in 400-D space correlations in 400-D space

• Data doubles every year• Caused by the emergence

of generations ofinexpensive sensors + computing

Why Is Astronomy Special?

• Especially attractive for the wide public• Community is not very large• It has no commercial value

– No privacy concerns, freely share results with others– Great for experimenting with algorithms

• It is real and well documented– High-dimensional (with confidence intervals)– Spatial, temporal

• Diverse and distributed– Many different instruments from

many different places and many different times

• The questions are interesting• There is a lot of it (soon petabytes)

Goal Create the most detailed map of the Northern sky

“The Cosmic Genome Project”Two surveys in one Photometric survey in 5 bands Spectroscopic redshift surveyAutomated data reduction 150 man-years of developmentHigh data volume 40 TB of raw data 5 TB processed catalogs Data is public2.5 Terapixels of images

Sloan Digital Sky Survey

The University of Chicago Princeton University The Johns Hopkins University The University of Washington New Mexico State University Fermi National Accelerator Laboratory US Naval Observatory The Japanese Participation Group The Institute for Advanced Study Max Planck Inst, Heidelberg

Sloan Foundation, NSF, DOE, NASA

The University of Chicago Princeton University The Johns Hopkins University The University of Washington New Mexico State University Fermi National Accelerator Laboratory US Naval Observatory The Japanese Participation Group The Institute for Advanced Study Max Planck Inst, Heidelberg

Sloan Foundation, NSF, DOE, NASA

Continuous data rate of 8 Mbytes/sec

Northern Galactic Cap drift scan of 10,000 square degrees 5 broad-band filters exposure time: 55 sec pixel size: 0.4 arcsec astrometry: 60 mas calibration: 2% at r'=19.8 done only in best seeing

(20 nights/year) Southern Galactic Cap multiple scans (> 30 times) of the same stripe

The Photometric Survey

u‘ g' r‘ i ' z’ 22.3 23.3 23.1 22.3 20.8 u‘ g' r‘ i ' z’ 22.3 23.3 23.1 22.3 20.8

Survey Strategy

Overlapping 2.5 degree wide stripesAvoiding the Galactic Plane (dust)Multiple exposures on Southern stripes

Overlapping 2.5 degree wide stripesAvoiding the Galactic Plane (dust)Multiple exposures on Southern stripes

SDSS Redshift Survey1 million galaxies 900,000 r’ limited 100,000 red galaxies volume limited to z=0.45100,000 quasars100,000 stars

Two high throughput spectrographsspectral range 3900-9200 Å640 spectra simultaneouslyR=2000 resolution, 1.3 Å

FeaturesAutomated reduction of spectraVery high sampling density and completenessObjects in other catalogs also targeted

The Spectroscopic Survey

Data Processing Pipelines

Analyzing the SkyServer

• Prototype in data publishing– 350 million web hits in 6 years– 930,000 distinct users

vs 10,000 astronomers– Delivered 50,000 hours

of lectures to high schoolstudents

– Delivered 100B rows of data– Everything is a power law

• GalaxyZoo– 27 million visual galaxy classifications by the public– Enormous publicity (CNN, Times, W.Post, BBC)– 100,000 people participating

Skyserver Sessions

Singh et al (2007)

Trends

CMB Surveys (pixels)• 1990 COBE 1000• 2000 Boomerang 10,000• 2002 CBI 50,000• 2003 WMAP 1 Million• 2008 Planck 10 Million

Galaxy Redshift Surveys (obj)• 1986 CfA 3500• 1996 LCRS 23000• 2003 2dF 250000• 2005 SDSS 750000

Angular Galaxy Surveys (obj)• 1970 Lick 1M• 1990 APM 2M• 2005 SDSS 200M• 2008 VISTA 1000M• 2012 LSST 3000M

Time Domain• QUEST• SDSS Extension survey• Dark Energy Camera• PanStarrs• SNAP…• LSST…

Petabytes/year by the end of the decade…

National Virtual Observatory

• NSF ITR project, “Building the Framework for the National Virtual Observatory” is a collaboration of 17 funded and 3 unfunded organizations– Astronomy data centers– National observatories– Supercomputer centers– University departments– Computer science/information technology specialists

• Similar projects now in 15 countries world-wide

=> International Virtual Observatory Alliance

Continuing Growth

How long does the data growth continue?• High end always linear• Exponential comes from technology + economics

rapidly changing generations– like CCD’s replacing plates, and become ever cheaper

• How many new generations of instruments are left?• Are there new growth areas emerging?• Software (collaboration) is becoming an instrument

– hierarchical data replication– Value added data/ mashups– data cloning

Technology+Sociology+Economics

• Neither of them is enough– We have technology changing very rapidly– Sensors, Moore's Law– Trend driven by changing generations of technologies

• Sociology is changing in unpredictable ways– In general, people will use a new technology if it is

• Offers something entirely new

• Or substantially cheaper

• Or substantially simpler

• Funding is essentially level

Surveys from Arecibo

• Facility very suitable for observing known sourcesor with known redshift in the ’local’ universe

• Perfect match to SDSS galaxies (<z>~0.1)• Matching sky coverage of SDSS, GALEX and FIRST• Enormous benefit from using new detector

technologies (focal plane phased array)• Possible large scale survey projects:

– Virgo Deep– SDSS+GALEX HI survey– Integrated HI in distant clusters (vs z)– Local universe (<10,000 km/s)

Summary

• Science is aggregating into ever larger projects• Collection of data is separating from science analysis• Much of recent evolution is through new sensors• VO is inevitable, a new way of doing science• Present on every physical scale today, not just

astronomy (Earth/Oceans, Biology, MS, HEP)• Might be the only way to do 'small science' in 2020