Scientific Motivations for the VO

• Historical Remarks on Massive Data Collection Projects.

• (Obvious) Potential Virtues and Defects of the VO for Observations of the Real World.

• State of the Simulated World.

• (Less Obvious) Potential Virtues and Defects of Archiving the Simulated World.

GarchingJune, 2002JPO

Astronomy vs Physics (a caricature)

• Physics• Designed to purpose

experiment.• Tightly controlled

conditions.• Quantitative

measurements.• Hypothesis testing.

• Astronomy• Designed to purpose

instrument.• Broad Survey.• Quantitative

measurements.• Exploration mode.

ManyNumbers

A Number

Ast vs Physics (contd.)

• Primary results always published by experimentalist.

• Long term use of experimental data is minimal.

• Many results obtained by outside users of surveys.

• Very long term viability of data.

ArchivingOf Modest

Utility

Great UtilityOf Well Done

Survey

Archived Astronomical Data

• Public Funding Public Access.• Rapid Growth in Large Area Detectors.• Fast Growth in Telescope Collecting Area.• Very Rapid Growth in Cyber-infrastructure: Data-Base Software, Networking, Cycles…

Extremely rapid e-folding of publiclyAccessible Data-bases

Some Virtues and Defects of VO

• Some Plusses

- More eyes on data.

More insight.

- More access.

More democracy.

- Multi-wavelength data.

Broader Astronomers.

- Better Software.

Easier theoretical analysis.

• Some Minuses

- Costly programs.

Resources diverted.

- Ignorance of sys errors.

False positive results.

- Less exclusivity.

Discourage instrument developers.

State of the Simulated World • Dark matter simulations

-methods include direct sum, tree and fftwith combinations of these most efficient,using domain decomposition and adaptive time stepping. Massive parallelization.

-state of the art is a mass resolution ofN = 1024^3 = 10^9 and spatial dynamic range of L/L = 10^5.

-e.g. (L,L)=(320mpc,3.2kpc); M = 10^9.4Msol,with 10^6 particles per cluster and 500 clusters.

Fly-Through a 1024^3 LCDM Dark Matter Simulation

Output of approximately 50 TB

Testing Cosmological Models:Gravitational Lensing

z<3Lbox~64 MpcDbox >> Lbox

Source Plane Image Plane

Gravitational Distortion of Distant Images

State of the Simulated World • Hydrodynamic simulations

-methods include mesh, moving mesh, adaptive mesh and SPH. Typically higher spatial resolution lower mass resolution.

-state of the art is a mass resolution ofN = 1024^3 = 10^9 (TVD), and spatial dynamic range of L/L = 10^4 (SPH, AMR).

Computing the Universe

• Transformation to co-moving coordinates x=r/a(t).

• Co-moving cube, periodic boundary conditions.

• Lbox >>nl

>> 20h-1/(1+z)^1.5 Lbox

Physics Input (to box)

• Newtonian gravity.• Standard equations of hydrodynamics• Atomic physics:adiabatic, + cooling,

+heating, + non-equilibrium ionization.• Radiative transfer: global average,

+shielding of sinks, +distribution of sources.• --------------------------------------------------• Maxwell’s equations in MHD form.

Physics Input Missing(important on galactic scales)

• Cosmic ray pressure and heating.

• Dust grain physics (depletion, absorption and catalyzation).

• Magnetic field generation.

• Multiphase media.

E.g., galaxy cluster formationdark matter density

(40 < z < 0)baryonic gas density

(40 < z < 0)

32 Megaparsec Bode, Cen, Ostriker & Xu

Animation (double click)

Origin of X-Ray Emission in Clusters of Galaxies

Animation (double click)log(T) at z=0

QSO Line Absorption from IGM

• TVDPM on Large Eulerian grids.

• Moderate over-density gas.

• Metals, ionization state computed.

• Line numbers and

profiles computed.

Hot gas filaments in the intergalactic mediumCen & Ostriker .

Simulated Spectrum

Star Formation Algorithm

• Consider gas that is dense, cooling and collapsing.

• Make stellar particle: M* = Mgas x t/Max(Tcool,Tdyn).

• Label particle with position, mass, metallicity and epoch.

• Give particle velocity of gas and follow dynamics as if dark matter particle.

Feedback from Stars

• Make star-cluster (eg Salpeter mass function) from stellar particle (M, Z, Tform).

• Age cluster and compute UV, winds, SN and metal ejection to IGM.

• Standard stellar evolution theory + one free parameter: M(high mass stars)/or “yield”, that is fixed by final metallicity.

Star Formation Cosmic History

Simulation Successes (to date)

• Lyman alpha cloud properties (column and red-shift distributions, line shapes, spatial correlations etc).

• Global star-formation history.

• Gross features of large-scale structure (voids and filaments, proper velocities, clustering properties etc).

Success (coming soon)

• X-Ray cluster gas properties (T ,Z, Lx etc).

• Secondary CBR effects (SZ, OV etc).

• Damped lyman alpha systems.

• Large splitting lensing.

• Metal enrichment history and density dependence.

Failure

Formation of galaxies with observed properties!

Archive Simulations(a virtual, virtual observatory?)

• Dark Matter Simulations

- Highly developed art, practitioners agree (largely) on results.

- Make suite of models (varying scale, cosmological model etc) available for comparison with observations.

Archive Simulations (contd)

• Hydrodynamic Simulations - Gas phase results: comparison with

observations helpful in judging models & planning new observations (eg Warm-Hot gas).

- Galaxy results: comparisons among simulators useful; comparisons to observations preliminary but helpful.

Summary

• On balance, VO provides great opportunity, but caution on side effects warranted.

• Parallel effort to archive and widely distribute results of increasingly realistic simulations worth consideration.