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The Virtual Observatory: CoreCapabilities and Support for

Statistical Analyses in Astronomy

THE US NATIONAL VIRTUAL OBSERVATORY

Robert Hanisch

US National Virtual Observatory

Space Telescope Science Institute

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Overview

The objective of the Virtual Observatory is to enable new science by greatly enhancing access to data and computing resources. The VO is intended to make it easy to locate, retrieve, and analyze data from archives and catalogs worldwide.

• Motivation; who’s involved; technical challenges and approach; capabilities

• Statistics in the VO• Future

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Astronomy is facing a data avalanche

Multi-Terabyte (soon: multi-Petabyte) sky surveys and archives over a broad range of wavelengths

Billions of sources, hundreds of attributes per source

1 nanoSky (HDF-S)

1 microSky (DPOSS)

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The changing face of observational astronomy

• Large digital sky surveys are becoming dominant source of data in astronomy: > 100 TB, growing rapidly– SDSS, 2MASS, DPOSS, GSC, FIRST, NVSS, RASS, IRAS,

QUEST, GALEX, SST; CMBR experiments; Microlensing experiments; NEAT, LONEOS, and other searches for Solar system objects

– Digital libraries: ADS, astro-ph, NED, CDS, NSSDC

– Observatory archives: HST, CXO, space and ground-based

– Future: PanSTARRS, LSST, and other synoptic surveys; astrometric missions, GW detectors

• Data sets orders of magnitude larger, more complex, more homogeneous than in the past

• Roughly 1 TB/Sky/band/epoch– Human Genome is < 1 GB, Library of Congress ~ 20 TB

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Threads of the the VO Fabric

Multiwavelength astrophysics

Archival Research

Survey astronomy

Temporal astronomy

NGC3104

Moore

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Who is the National Virtual Observatory?

• US NVO development project, funded by NSF Information Technology Program and managed by NSF Astronomy Division, is in final year of 5-year project

• Funding is $10M+ over the 5 years• 17 organizations (astro, CS, IT) involved

– JHU (PI Alex Szalay), STScI, Caltech (Astronomy, IPAC, CACR), HEASARC, SAO, NRAO, NOAO, NCSA, SDSC, FNAL, USNO, et al.

• Collaboration with Gemini, LSST, et al.

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International collaboration

• NVO is co-founder of the International Virtual Observatory Alliance

• IVOA now has 16 member projects• Adopted a standards process based on W3C• Forum for discussion and sharing of experience

http://ivoa.net

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Interoperability

VizieR: Contains more than 4000 astronomical catalogues consisting of one or several tables.

Problem: as the catalogues come from many different sources, the original descriptions are very heterogeneous: “Give me all tables containing the V magnitude in the Johnson system.” 144 different names for Johnson V !

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Interoperability challenges

• Metadata standards• Data discovery• Data requests• Data delivery• Units• Database queries• Distributed applications; web services• Authentication and authorization

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RegistriesNVO Resource

Discovery

Computational Services

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Catalogs, Archives, Collections, Models

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Architecture

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NVO Components

• Data discovery and location– Resource Registry: Organizations, archives, tables, databases,

services– Footprint Services

• Data access– Simple tables and observation logs: Cone Search– Images: Simple Image Access Protocol (SIAP)– Spectra: Simple Spectrum Access Protocol (SSAP)VOTables and FITS used to exchange data throughout the VO– Databases: SkyNode, with Astronomical Data Query Language

(ADQL)– Transient events: VOEvent protocol– Data models, Space-Time Coordinates (STC)

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NVO Components

• Distributed data storage– VOStore, VOSpace– Authentication and authorization

• Distributed computing– Web services– Grid services– Scalability

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NVO Applications

• Registry Interface• DataScope• Coverage Maps• Open SkyQuery• WESIX (SExtractor)• WCS Fixer• Spectrum Services• VOEvent Net• Montage mosaics• Integration with legacy software systems

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NVO Registry Portal

Find source catalogs, image archives, and other astronomical resources registered with the NVO

A Registry is a distributed database of Virtual Observatory resources: primarily access services for catalog, image, and spectral data, but also descriptions of organizations and data collections. There are several coordinated registry implementations that share information by harvesting each other's resources. This registry is at STScI in Baltimore, MD.Searches for resources can be done by keyword, or advanced queries can be expressed in the SQL language. The registry is open for humans through web forms, or machines through SOAP web services.

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DataScope

Using the NVO DataScope scientists can discover and explore hundreds of data resources available in the Virtual Observatory. DataScope uses the VO registry and VO access protocols to link to archives and catalogs around the world. Users can immediately discover what is known about a given region of the sky: they can view survey images from the radio through the X-ray, explore archived observations from multiple archives, find recent articles describing analysis of data in the region, find known interesting or peculiar

Discover and explore data in the Virtual Observatory

objects and survey datasets that cover the region. A summary page provides a quick précis of all of the available data. Users can download images and tables for further analysis on their local machines, or they can go directly to a growing set of VO enabled analysis tools, including Aladin, OASIS, VOPlot and VOStat.

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Open SkyQuery

Cross-match your data with numerous catalogs

OpenSkyQuery allows you to cross-match astronomical catalogs and select subsets of catalogs with a general and powerful query language. You can also import a personal catalog of objects and cross-match it against selected databases.

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Spectrum Services

Search, plot, and retrieve SDSS, 2dF, and other spectraThe Spectrum Services web site is dedicated to spectrum related VO services. On this site you will find tools and tutorials on how to access close to 500,000 spectra from the Sloan Digital Sky Survey (SDSS DR1) and the 2 degree Field redshift survey (2dFGRS). The services are open to everyone to publish their own spectra in the same framework. Reading the tutorials on XML Web Services, you can learn how to integrate the 45 GB spectrum and passband database with your programs with few lines of code.

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Web Enabled Source Identification with Cross-Matching (WESIX)

Upload images to SExtractor and cross-correlate the objects found with selected survey catalogs.

This NVO service does source extraction and cross-matching for any astrometric FITS image. The user uploads a FITS image, and the remote service runs the SExtractor software for source extraction. The resulting catalog can be cross-matched with any of several major surveys, and the results returned as a VOTable. The web page also allows use of Aladin or VOPlot to visualize results.

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Coverage Maps

The NVO Sky Statistics Service generates source counts, coverage maps, and links to downloadable data for catalog holdings available through the NVO protocols, including IRSA, NED and CDS VizieR

View catalog coverage maps and source inventories for a position or object of interest.

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WCS Fixer

Repair image coordinates in images with inaccurate or misaligned coordinate systems.

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VOEvent NetExplore the multiwavelength sky in the vicinity of transient events.

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Montage Mosaics

Make mosaics from 2MASS, DPOSS, or SDSS images.

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VO Tools

• VOTable display and analysis– VOPlot, TOPCAT, Mirage

• Image display and analysis– Aladin, OASIS– Other standard display tools for downloaded data

• Spectrum display and analysis– VOSpec, SpecView

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Statistics and the VO…

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From single objects…

• Observations of small, carefully selected samples (often with a priori prejudices) of objects in one or a few wavelength bands

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…to large-scale statistical studies

• Multi-wavelength data for millions of objects, allowing us to:– Discover significant patterns from the analysis of statistically

rich and unbiased image/catalog databases – Understand complex astrophysical systems via confrontation

between data and sophisticated numerical simulation

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VO-aware statistics tools: VOPlot

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VO-aware statistics tools: VOPlot

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VO-aware statistics tools: VOPlot

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VO-aware statistics tools: TOPCAT

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VO-aware statistics tools: TOPCAT

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VO-aware statistics tools: TOPCAT

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VO-aware statistics tools: TOPCAT

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Pairwise plots

Box plots

K-means

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Statistics in the VO

• What more is needed?– Scalability: Extend analysis to 10^9 measurements or

more– Operate on data where it resides– VOSpace

• Probabilistic cross-matching

€

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Statistics in the VO

• Image stacking– White et al. (2006) detect radio counterparts to SDSS

QSOs at level 30X below rms noise via median stacking of 41,000 FIRST images

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Next steps

• NVO Facility– Joint NASA/NSF program, operations to begin in 2007– Partnership between NASA data centers, major ground-

based observatories, university research groups.

Need to define the requirements for VO-enabled statistical analysis.

• VO concept is being adopted broadly– AGU special session on VOs– NASA solicitation for Virtual Observatories for Solar and

Space Physics Data (VxOs); AISRP support for VO technology

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http://us-vo.org/