A Hubble Sphere Hydrogen Survey Jeff Peterson and Kevin Bandura (CMU) Ue-Li Pen (CITA) Uros Seljak (Princeton and Trieste) Chris Blake (UBC) Astroph N

Introduction Hydrogen is most abundant element in the universe, 21cm (1.4 GHz) hyperfine transition unabsorbed through to horizon. 3-D maps. Map of the visible universe: economic and fast with transit cylinders. Cosmological parameters: standard yardstick from baryon oscillations, weak lensing sources

Nuclear Hyperfine Transition of Hydrogen Electron-proton magnetic moment coupling in H ground state ΔE=½α 5 m e c MHz

Image courtesy of NRAO/A UI and Chung et al., Columbia Universit y

Limits to Cosmology CMB, lensing, galaxy survey: Power spectra sample variance (cosmic variance). For CMB, statistical accuracy ~ 1/l max, -> parameter errors > Other methods (SNe, clusters) in progress, accuracy unlikely higher, except possibly CMB polarization. Of theoretical interest: dark energy, 2nd order PT, gravity waves. Can such accuracy be achieved observationally?

Visible Universe Redshift Survey SDSS, 2dF map to z~0.1 Factor of 10 further to z>1 Cosmic power spectrum: baryon oscillations: dark energy Weak lensing: dark matter inventory/map Pulsar Timing Array seach for Gravity Waves

Hubble Sphere Hydrogen Survey Strategy: targeted, fast, survey experiment (c.f. CMB: CBI, DASI, SPT, ACT) Power spectra, SNR=1 (c.f.CMB), not 10. cosmic magnification, Zhang and Pen 2005, PRL 95, All sky transit (c.f. LMT)

Traditional Radio Telescope Cost Drivers High Frequency: cryogenic receivers, surface, pointing accuracy Correlation/bandwidth: N 2 cost General purpose – steerable, reconfigurable HSHS target: $10/m 2, <1.4 GHz, transit GMRT actual: $100/m 2, <1.4 GHz SKA target: $1000/m 2 VLA actual: $10000/m 2

Indian Giant Meterwave Radio Telescope 30 ea. Operates GHz Collaborators: Y. Gupta (chief scientist), Rajaram Nityananda (director), R. Subramanian, S. Sethi, A. Roshi (Raman), C. Hirata (IAS), T. Chang (UCB)

Program -Use acoustic oscillations from z = 0 to z = 1.5 to detail the transition from deceleration to acceleration. -Survey 21 cm emission over >2 Pi steradians from 500 to 1500 MHZ with a 400,000 sq m fixed-pointed meridian- scan radio telescope. -Fixed Cylindrical Reflectors allow for ultra-wide field observations, and inexpensive FFT based beam forming. -Modest construction cost--$20M--$0.02/redshift NGC 3149

The Universe is Accelerating But it must have been decelerating in the past. Acoustic oscillations give us the “standard ruler” to follow this transition.

Baryon Wiggles Detected by SDSS and 2df

Projected W and W’ sensitivity Blake and Glazebrook

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 limitation: 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

Cylindrical reflectors use suspended mesh, with a line of feed points Reflector Cost: ~$20/m^2 Survey Speed~A*D

Existing cylinders MOLONGLO Cost:$12/m^2 (current dollars) OOTY Both rotate in one dimension Molonglo AUSTRALIA Brisbane Darwin Perth Canberra Hobart Adelaide Melbourne Sydney +

Cylinder History Popular Lost favor with advent of cryogenically cooled pre-amplifiers. Room temp amplifiers with 20K noise temp now available. Illinois 400 ft Telescope ca. 1960

Beam Former Signal Flow FFT vs t Transpose gigE switch FFT vs t 1024 ADCs/cyl, 8- way analog sum … FFT vs y XMAC vs x Cost: 200MS/s x 4 cyl x 1024 ch x 2 FFT’s x 10(log 2 ) x 2.5 = 41 Tips Software correlator: $300 for 40 Gips (peak) node, efficiency = 0.5, $15000/sustained Tip. Plus electricity cost (2MWh/yr/node). On 50m wide cyl, one computer per 2m length. FPGA reduces power consumption.

Software correlator

Additional Science Find and monitor 1000s of new pulsars- -strongly constrain the gravity wave background Map galactic magnetic fields Study Early Ionization at z > 6

Prototype cylinders are under construction

Conclusions Using off-the-shelf technology, a redshift survey telescope can be built for modest cost ($20M) which will yield 10^9 redshifts to z~1.5. Major data processing, electronics challenge. Targeted science, not general purpose telescope. Quiet site desirable Will cover 100 times the SDSS volume Map baryon oscillations, dark matter (lensing). Will constrain w 1 to ~0.1