# Presentation: 468167

## Rise and Fall of HI

- Ue-Li Pen 彭威礼

- Jeff Peterson, CMU

- Radiative Xfer simulation by Iliev, Mellema & Pen

## Search for Cosmic Hydrogen

- About half of horizon volume filled with HI, dominated by z>6
- hi-z: lots out there, structures with up to 1016 Mסּ HI.  Difficult to observe window, foregrounds.
- Mid-z: neutral HI in galaxies, 0.1<z<2.  Billions of galaxies, HI mass function evolution poorly known.  Intrinsically faint (μJy), requires large collecting area (>105 m2).  GMRT/SKA.

- Image courtesy of NRAO/AUI and Chung et al., Columbia University

## Traditional Radio Telescope Cost Drivers

- High Frequency: cryogenic receivers, surface, pointing accuracy
- Correlation/bandwidth: N2 cost
- General purpose – steerable, reconfigurable
- HSHS target:  $10/m2, <1.4 GHz, transit
- Molonglo actual: $12/m2, steerable cyl
- GMRT actual: $100/m2, <1.4 GHz
- SKA target:  $1000/m2
- VLA actual: $10000/m2

## HSHS: Large Area, Low Cost

- Surface: low frequency mesh (GMRT)
- Structure: passive transit cylinder
- Correlations: FFT is N log N  instead of N2
- Signal processing: PC’s are $3/Gflop
- Astro-ph/0606104

## Existing operational cylinders

- MOLONGLO
- 1600x12m
- Cost:$12/m2
-  (current dollars)

- OOTY
- 530x30m
- Both rotate in one
- dimension

## Cylinder History

- Popular 1960-1980
- Lost favor with advent of cryogenically cooled pre-amplifiers.
- Room temp amplifiers with 20K noise temp now available.

- Illinois 400 ft
- Telescope
- ca. 1960

## Local HI Luminosity Function

- Zwann et al

-  at z=1.5 this is 30 microjansky
- We detect all these across 1/2 of sky in 6 months

## Cosmic Magnification

- Cosmic shear has evolved as a direct way to map dark matter
- Several major surveys under way or planned – CFHTLS, LSST, SNAP
- Anticipated limitations: redshift distribution, PSF
- With redshifts, these limits can be overcome, and magnification is measured directly
- Measured through cross correlation in SDSS (Scranton *et al* 2005)
- Forecasts and models by Zhang and Pen (2005, 2006): overcomes intrinsic clustering.

## Gravitational Lensing: increase flux, decrease density

- Magnification: increases number of bright galaxies, decreases faint ones.

## Four Cylinders each 2 km long, 50m wide

- Line feeds at foci used to create 4000 beams

- N

- 2 km

## CMU Prototype cylinders under construction. Funded by Seljak/Packard

## Sept 17 status

## Line Feed

- LNA, $1.81

- Filters,
- $1.99 ea.

## Additional Science

- Find and monitor 1000s of new pulsars--strongly constrain the gravity wave background
- Map galactic magnetic fields
- Study Early Ionization at z > 13

## Pros and Cons of 21-cm Cylinder Scheme

- Off the shelf technology
- Low Cost
- Fast Constructions
- Expandable in area and field of view
- Expandable in Science Goal
- Astronomical Sources have clean signature
- Negligible 21 cm confusion
- 21 cm luminosity likely higher in the past

- Low Cost
- RFI unknown
- Intermodulation possible
- Cost not demonstrated
- 21 cm luminosity function at high z unknown

## HI Evolution

- Major cost uncertainty is luminosity function evolution.
- Popular models differ by factor of several
- Effort under way to measure z=1.4 mass function using DEEP cross correlation (T. Chang, M. Davis, U. Seljak)

## WMAP 3yr: rise of HI

- τ=0.09+/-0.03, zr=11

- Cosmic precombination

- White et al 2003: universe fully ionized at z<6

- Barkana & Loeb 2001

## Reionization

- First objects:
- 21cm @ z=6-15
- 90-200 Mhz
- ΔT = 23 mK,
- ~μJy- mJy (up to 1016 Mסּ of HI)
- Angular scale 5’<Θ<30’, freq res 500 khz
- Challenging theory

- z=19-12 simulation, Iliev, Mellema, Pen 2005. 1o FOV

## Cosmic Reioniation

- Largest radiative transfer cosmological reionization simulations: 1 degree FOV.
- Detection in 21cm hyperfine transition with radio telescopes.  Structure on large scales (>20’).
- Iliev, Mellema, Pen 2006

## Foreground: Galactic Synchrotron

- Haslam 408 MHz

- Much brighter than signal, but no spectral structure

## Detectability

- Luminosity proportional to object volume: bigger structures easier to find
- Noise dominated by galaxy: T=300(ν/150 Mhz)-2.5, higher frequency (lower redshift) much easier
- Mean emission challenging to discern (Gnedin and Shaver 2004).
- First targets: Stromgren spheres around bright quasars (Wyithe and Loeb 2004).

## First Light Experiments

- Existing w/prelim data: PAST/21CMA (China), GMRT (India)
- Under construction: LOFAR (Netherlands), MWA (Australia), T-rex (Canada), CorE (Australia), VLA-VHF (USA)
- Future: SKA, JWST

- LOFAR

## Mileura Wide-angle Array

- Photos: Brian Corey and Eric Kratzenberg, MIT Haystack Observatory

- Indian Giant Meterwave Radio Telescope

- 30 dishes @45m ea.
- Operates in 2m band
- Collaborators: Y. Gupta (chief scientist), Rajaram Nityananda (director), R. Subramanian, S. Sethi, A. Roshi (Raman), C. Hirata (IAS), T. Chang (UCB)

## GMRT Search

- Operating telescope, 50000m2, up to 32 Mhz BW, fully polarized, lowest band 100-200 Mhz.  Biggest collecting area in this band.
- Half in central 1km core, rest in 50 km Y.
- Currently hits RFI limit after a few minutes of integration: power lines, TV stations, HAM amateurs, faulty home electronics.
- Exploration of new RFI mitigation schemes, software correlator, nearfield clean.
- Search for SDSS QSO Stromgren spheres in TV band: 6 antenna filters already replaced.

- GMRT 150 Mhz image
- By Ishwara Chandra (NCRA)
- Image noise 2 mJy
- Thermal limit 0.5 mJy

## Software correlator: $300/node

## Power Line Noise

- Time-lag: Folded 70ms data on short baseline

## CMB

- Comoving distances

- reionization

- Low l anomaly: model primary CMB to l~20

- EoR

*ISW: lensing map predictions*

- T-E correlations: can be predicted!

- Pen 2003

## Potential Theoretical Benefits

- Precision measurement of power spectrum at 10-8 accuracy (beyond PAST)
- Dark energy dynamics: q0, a(t), ISW, dark matter dynamics/clustering (through lensing), gravity waves.
- Initial conditions: 2nd order inflation effects, backreaction, curvature, etc. (through hydrogen matter P(k) and 3pcf).

## Outlook

- Existing constraints: optical depth from WMAP, SDSS QSO’s.
- Theoretical progress: direct simulations indicate power on larger scales (>20’), making detections more tractable.
- current: initial data from Past/21CMA and GMRT, data analysis, ionospheric solution (Hirata).
- Several other experiments developing: LOFAR, VLA/VHF
- Bright outlook: several experiments underway or planned to tap the next cosmic horizon
- Exciting new window on universe for precision cosmology.  Open field for theory and experiment.