title people CHIME: the Canadian Hydrogen Intensity Mapping Experiment. Mark Halpern Kris Sigurdson Sigi Stiemer Tom Landecker Jeff Peterson Dick Bond Ue-Li Penn Matt Dobbs David Hanna UBC DRAO Carnegie Mellon CITA McGill

title people We have proposed to build a new telescope, CHIME, to study Baryon Acoustic Oscillations at the DRAO. The telescope will consist of 5 NS cylindrical reflectors coupled to a large digital correlator and will perform hydrogen intensity mapping of redshifted 21cm radiation. Plan of the talk: 1. What are Baryon Acoustic Oscillations? 2. What will CHIME look like?

Evolution of a density spike in co-moving coordinates. Notice when neutrinos and then photons decouple from baryons. Animation: SDSS Collaboration

Eisenstein et al ApJ

107/h = 148 h= 0.72 Eisenstein et al ApJ

BAO have, of course, been seen in the CMB. They form the “shape” of each hot or cold spot. Komatsu et al Bennett et al. 2010

2.The cosmological constant is only one possibility for the nature of dark energy. In a  dominated universe pressure is negative: P/  w, but in general w can be a function of time or redshift, w(z). To measure how w(z) evolves we need to measure at least one of: A. Angular sizes of a distribution of standard rulers; B. Brightnesses of a distribution of standard candles; or C. Weak lensing patterns. CHIME will supply option A.

DETF Figure of Merit Marginalize over all other parameters and find uncertainties in w  and w a  CDM value w ( a ) = w   w a (  a ) w  w  today & w  w   w a in the far past  DE  DE (today) exp {   [  w (a) ] d ln a }  CDM: w (a)  DETF FoM  1./(area of ellipse) = 450 for the nominal CHIME If built now, CHIME will deliver precision at a tiny cost and well ahead of any competitive experiment.

Figure of Merit for an HI measurement from z 1 to z 2. Given the cell phone wall at 800 MHz, corresponding to z 1 =0.8, there is not much advantage to push the lower freq. Limit beyond z 2 =2.5, or 400 MHz Pushing BAO measurements to low redshift drives the ultimate sensitivity of a survey.

Frequency shift corresp. to  z Redshift d c-m further away. Resolution at z of a 100m telescope The size and frequency resolution of CHIME are chosen to resolve Baryon Acoustic Oscillations in three dimensions. Freq. of redshifted 21cm radiation

CHIME will consist of five 20m x 100m cylindrical reflectors with feeds, amplifiers and digitizers spaced along the 100m focal line.

We have built room temperature amplifiers for CHIME which are much quieter than we had assumed for our sensitivity estimates. This is the work of Greg Davis, UBC.

A CHIME amplifier.

The measured RF Interference at the proposed CHIME site at the DRAO in Penticton looks promising. Measured December 2009 Measurement resolution is 10 kHz. The cell phone band at 850 GHz defines CHIME’s top frequency. Test noise floor is 400K.

CHIME anticipated sensitivity at z=1.5, two years of data. Error bars grow at the right due to finite angular resolution and at the left because CHIME only surveys 40% of the sky Spectrum w. BAO Spectrum w.o. BAO

CHIME will produce data a decade earlier than experiments of comparable sensitivity, and for 1-10% of the cost. Expt. “shot noise” is proportional to survey volume.

We will need a feed every ~25 cm which couples to our f/.25 reflector in one direction and has a more limited field of view along the axis. The crossed bow-tie style of antenna developed by the West Virginia Antenna Group and tested on Molonglo seems attractive for cost reasons. They can be made from printed circuit boards. From Leung, Kot and Jones