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Neutral Hydrogen at High RedshiftPowerPoint Presentation

Neutral Hydrogen at High Redshift

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Presentation Transcript

Agenda

- Brief introduction and current knowledge
- N-Body simulations and models
- Projected integration times
- Techniques of detection (Instruments)
- Results and conclusions

Introduction

- HI at large z
- HI is uniformly distributed at z >> 20

- Current observations
- Show galaxies from z = 5 to 0

- What is going on from z = 20 to z = 5?
- HI probes could constrain formation models
- When did the IGM become ionized?

Current Knowledge

- First star clusters form at z ~ 20
- UV radiation from first generation clusters ionizes HI
- IGM is completely ionized at z < 5

- HI exists only in dense clumps due to high column density
- No direct observations from z = 20 to z = 5

HI at current epoch

- Watch the movie

Phases of HI

- Current/Late Epoch (5 < z < 0)
- IGM completely ionized
- HI exists in dense clumps

- Early Epoch (z >> 20)
- Uniformly distributed
- No ionization

Phases of HI

- Intermediate Epoch (20 < z < 5)
- Ionized Phase
- Same as the current epoch

- Warm Phase
- HI has been reheated by first stars
- No reionization
- Spin temperature >> CMB temperature
- Observed in redshifted 21 cm radiation

- Ionized Phase

Phases of HI

- Intermediate Epoch (20 < z < 5)
- Cold Phase
- Far from sources of radiation
- No reionization, no reheating
- Spin temperature ~ CMB temperature
- No radiation expected

- Cold Phase

What We Need to Detect

- Need to detect the fluctuations of redshifted 21 cm radiation
- Need to predict the detection limit
- Use N-Body simulations to generate maps

- What instrument could reach that level?

N-Body Simulations

- 1283 particles
- Each “particle” has M = 2.7 x 1011 Ω0 MSun

- 1283 mesh
- Physical size = 128 h-1 Mpc

- Variety of models can be implemented

Potential Problems

- Considering gravity only, no gas pressure
- Plays a role in small scale distribution and the state of the gas
- But only worried about large scale properties

- Assume HI assigned to a particle does not depend on the mass of the collapsed structure that contained it
- But we expect large structures to behave like groups of galaxies (i.e. less HI by fraction)
- Expect smaller structures to have less HI fraction due to photo-ionizing background

Models

- Standard CDM (sCDM)
- h = 0.5, Ω0 = 1, Γ= 0.5

- Mixed Dark Matter (MDM)
- h = 0.5, Ω0 = 1, Γ= 0.3

- Λ CDM (LCDM)
- h = 0.5, ΩΛ = 0.4, Γ= 0.3

- Others
- Open CDM, Tilted Einstein DeSitter

Choosing the Appropriate Model

- Reasons LCDM is preferred model
- Growth of perturbations slows down at late epochs
- Comoving volume enclosed in given solid angle at high redshifts is higher for a universe with nonzero Λ. This yields more emitters, and hence, a higher signal

MDM

LCDM

- All for z = 3.34
- MDM has less power at smaller angular scales
- sCDM and LCDM have comparable signals
- Physical size = 3 h-1 Mpc per pixel
- Contour Levels
- 15, 30, 60 μJy

- Simulated Radio Map for
- z = 5.1
- Physical Size = 5 h-1 Mpc per pixel
- Contour Levels
- 40, 80, 120, 200 μJy

- z = 5.1

- We see fewer small scale structures in the z = 5.1
- less small scale structures could be detected at larger redshifts, due to instrumental capabilities
- using these models, small scale formation may be taking place

Integration Times (GMRT)

- Start with the radiometer equation
- = (Tsys/T)2/

- For the GMRT:
- Converting Signal to Mass

Computing Integration Times

- Desire a 3 detection
- z = 3
- For GMRT this occurs for 3 – 6’ scales
- Requires 100 – 1000 hours for one beam

Are Detections Likely?

- Will there be structures in a GMRT beam?
- Volume of beam larger than that used in simulations
- Volume of beam much larger than volume of fields already observed (LBG’s)
- Spikes observed in both of these fields
- Conclusion: Spikes will be seen in GMRT beam

Future Telescopes

- Current telescopes inadequate
- Need something with a larger collecting area and a higher sensitivity
- Possibilities:
- GMRT – Giant Metre-wave Radio Telescope
- SKA – Square Kilometer Array
- LOFAR – Low Frequency Array

Instruments - GMRT

- Giant Metre-wave Radio Telescope
- 30 45m dishes
- 50 - 1500 MHz
- Located in India, to try to minimize man-made radio interference
- At 327 MHz, 8 times more sensitive than VLA
- 3 times the collecting area of the VLA

GMRT – Continued

- Central array consists 14 dishes in a 1 km2 region
- Angular resolution of 60” for lowest frequencies
- 435 baselines (VLA has 351)

Instruments - SKA

- Square Kilometer Array
- Not Completed
- .15 – 20 GHz
- Array of arrays: approximately 30 200m dishes
- Spread over 1000km
- Suitable for pencil beam surveys

Instruments - LOFAR

- Low Frequency Array
- 10 – 240 MHz
- 100 antennas in 1 system; 100 systems
- Full Operations – 2008
- Spread over 400km
- Capable of observing 11 > z > 3.5

Conclusions

- Epoch of 20 > z > 5 important in understanding structure formation
- No direct observations at z > 5
- At z = 5, IGM is completely ionized
- Use N-body simulations to determine predicted flux levels at these epochs
- Compare with levels observable using present technology

Conclusions

- Present day technology inadequate
- Need next generation telescopes
- GMRT (fully operational in next few years)
- SKA (~15 years)
- LOFAR (~2008)

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