scientific motivations for the vo historical remarks on massive data collection projects. (obvious)...
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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.