Neutral hydrogen at high redshift
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Neutral Hydrogen at High Redshift. Jared Bowden Dain Kavars. 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

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Neutral Hydrogen at High Redshift

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Neutral hydrogen at high redshift

Neutral Hydrogen at High Redshift

Jared Bowden

Dain Kavars


Agenda

Agenda

  • Brief introduction and current knowledge

  • N-Body simulations and models

  • Projected integration times

  • Techniques of detection (Instruments)

  • Results and conclusions


Introduction

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

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

HI at current epoch

  • Watch the movie


Phases of hi

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 hi1

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


Phases of hi2

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


What we need to detect

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

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

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

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


Neutral hydrogen at high redshift

z = 0

Solid Line: sCDM

Dash: MDM

Dot Dash: LCDM

z = 3.34


Choosing the appropriate model

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


Neutral hydrogen at high redshift

sCDM

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


Neutral hydrogen at high redshift

  • Simulated Radio Map for

  • z = 5.1

  • Physical Size = 5 h-1 Mpc per pixel

  • Contour Levels

    • 40, 80, 120, 200 μJy


Neutral hydrogen at high redshift

  • z = 3.34

  • 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

Integration Times (GMRT)

  • Start with the radiometer equation

    •  = (Tsys/T)2/

  • For the GMRT:

  • Converting Signal to Mass


Computing integration times

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

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


Current telescopes

Current Telescopes


Future telescopes

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

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


Instruments gmrt1

Instruments - GMRT


Gmrt continued

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

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 ska1

Instruments - SKA


Instruments lofar

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


Instruments lofar1

Instruments - LOFAR


Conclusions

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


Conclusions1

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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