Scientific Motivations for the VO

1. Garching June, 2002 JPO 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.

2. Physics Designed to purpose experiment. Tightly controlled conditions. Quantitative measurements. Hypothesis testing. Astronomy Designed to purpose instrument. Broad Survey. Quantitative measurements. Exploration mode. Astronomy vs Physics (a caricature) A Number Many Numbers

3. 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. Ast vs Physics (contd.) Great Utility Of Well Done Survey Archiving Of Modest Utility

4. Archived Astronomical Data • Public Funding a a 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 publicly Accessible Data-bases

5. Some Plusses - More eyes on data. a More insight. More access. a More democracy. Multi-wavelength data. a Broader Astronomers. Better Software. a Easier theoretical analysis. Some Minuses Costly programs. a Resources diverted. Ignorance of sys errors. a False positive results. Less exclusivity. a Discourage instrument developers. Some Virtues and Defects of VO

6. State of the Simulated World • Dark matter simulations -methods include direct sum, tree and fft with combinations of these most efficient, using domain decomposition and adaptive time stepping. Massive parallelization. -state of the art is a mass resolution of N = 1024^3 = 10^9 and spatial dynamic range of L/DL = 10^5. -e.g. (L,DL)=(320mpc,3.2kpc); DM = 10^9.4Msol, with 10^6 particles per cluster and 500 clusters.

7. Fly-Through a 1024^3 LCDM Dark Matter Simulation Output of approximately 50 TB

8. Testing Cosmological Models:Gravitational Lensing z<3 Lbox~64 Mpc Dbox >> Lbox

9. Gravitational Distortion of Distant Images Image Plane Source Plane

12. State of the Simulated World • Hydrodynamic simulations -methods include mesh, moving mesh, adaptive mesh and SPH. Typically higher spatial resolution a lower mass resolution. -state of the art is a mass resolution of N = 1024^3 = 10^9 (TVD), and spatial dynamic range of L/DL = 10^4 (SPH, AMR).

13. Computing the Universe • Transformation to co-moving coordinates x=r/a(t). • Co-moving cube, periodic boundary conditions. • Lbox >>lnl >> 20h-1/(1+z)^1.5 Lbox

14. 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.

15. Physics Input Missing(important on galactic scales) • Cosmic ray pressure and heating. • Dust grain physics (depletion, absorption and catalyzation). • Magnetic field generation. • Multiphase media.

16. E.g., galaxy cluster formation dark matter density (40 < z < 0) baryonic gas density (40 < z < 0) Animation (double click) 32 Megaparsec Bode, Cen, Ostriker & Xu

17. Origin of X-Ray Emission in Clusters of Galaxies log(T) at z=0 Animation (double click)

18. 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 medium Cen & Ostriker .

19. Simulated Spectrum

20. Star Formation Algorithm • Consider gas that is dense, cooling and collapsing. • Make stellar particle: DM* = DMgas x dt/Max(Tcool,Tdyn). • Label particle with position, mass, metallicity and epoch. • Give particle velocity of gas and follow dynamics as if dark matter particle.

21. Feedback from Stars • Make star-cluster (eg Salpeter mass function) from stellar particle (DM, Z, Tform). • Age cluster and compute UV, winds, SN and metal ejection to IGM. • Standard stellar evolution theory + one free parameter: DM(high mass stars)/DM*, or “yield”, that is fixed by final metallicity.

22. Star Formation Cosmic History

23. 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).

24. 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.

25. Failure Formation of galaxies with observed properties!

26. 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.

27. 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.

28. 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.